### ADDENDUM

USER'S GUIDE FOR THE
AMS/EPA REGULATORY MODEL - AERMOD (EPA-454/B-03-001, September 2004)

U.S. ENVIRONMENTAL PROTECTION AGENCY Office of Air Quality Planning and Standards Air Quality Assessment Division Research Triangle Park, North Carolina 27711

December 2012ii PREFACE

This document provides updated user instru ctions for the AERMOD dispersion model, including modifications introdu ced with version 06341 and later. This addendum supplements and updates the information contained in the current AERMOD User’s Guide (EPA, 2004a).iii ACKNOWLEDGEMENTS

Portions of this Addendum to the “User’s Guide for the AMS/EPA Regulatory Model –
AERMOD” related to the PSDCR EDIT option for the Plume Volume Molar Ratio Method (PVMRM) were prepared by MACTEC Federal Progr ams, Inc., Research Triangle Park, North Carolina. This effort was funded by the E nvironmental Protection Agency, Region 10, under Contract No. EP-D-05-096, with Herman Wong as the Work Assignment Manager (WAM).iv CONTENTS

PREFACE

............................................................................................................................. ii ACKNOWLEDGEMENTS ........................................................................................................ iii FIGURES

............................................................................................................................ vi TABLES ........................................................................................................................... v ii 1.0 INTRODUCTION ................................................................................................................... 1 1.1 OVERVIEW OF AERMOD REVISIONS ....................................................................... 1 1.2 BACKGROUND ON DEPOSITION ALGORITHMS ................................................... 6 2.0 USER INSTRUCTIONS ........................................................................................................ 9 2.1 DISPERSION MODELING OPTIONS ........................................................................... 9 2.1.1 Modification to Urban Opti on for Morning Transition ................................................. 9 2.1.2 MODELOPT Keyword ................................................................................................ 10 2.1.3 BETA Test Options...................................................................................................... 1 5 2.1.4 Averaging Time Options.............................................................................................. 16 2.1.5 Performing Multiple Year Analyses with MULTYEAR Option ................................. 17 2.1.6 Processing for Particulate Matter (PM) NAAQS ......................................................... 19 2.1.7 Processing for 1-hour NO 2 and SO 2 NAAQS .............................................................. 22 2.1.8 Specifying Multiple Urban Areas ................................................................................ 24 2.1.9 BETA Options for Capped and Ho rizontal Stack Releases ......................................... 25 2.1.10 BETA Options for Low Wind Conditions ................................................................. 27 2.2 DEPOSITION ALGORITHM INPUTS AND OPTIONS ............................................ 29 2.2.1 Definition of Seasons for Gas Dry Deposition ............................................................ 29 2.2.2 Definition of Land Use Categor ies for Gas Dry Deposition ........................................ 30 2.2.3 Option for Overriding Default Parameters for Gas Dry Deposition ............................ 31 2.2.4 Specifying Source Parameters for Ga s Deposition (Dry and/or Wet) ......................... 32 2.2.5 Option for Specifying the Deposition Velocity for Gas Dry Deposition..................... 33 2.2.6 Specifying Source Parameters for Particle Deposition ................................................ 33 2.2.7 Specifying Emission and Output Units ........................................................................ 35 2.2.8 Deposition Velocity and Resistance Outputs ............................................................... 36 2.2.9 Meteorological Data for Deposition Algorithms ......................................................... 37 2.3 OPEN PIT SOURCE OPTION ....................................................................................... 38 2.4 LINE SOURCE OPTION ................................................................................................ 41 2.5 SPECIFYING BACKGR OUND CONCENTRATIONS .............................................. 42 2.6 PVMRM AND OLM OPTIONS FOR MODELING NO 2 ............................................ 46 2.6.1 Specifying Ozone Concentrations for PVMRM and OLM Options ............................ 47 2.6.2 Specifying the Ambient Equilibrium NO 2 /NO x Ratio for PVMRM and OLM ........... 51 2.6.3 Specifying the Default In-stack NO 2 /NO x Ratio for PVMRM and OLM ................... 51 2.6.4 Specifying In-stack NO 2 /NO x Ratios by Source for PVMRM and OLM ................... 52 2.6.5 Specifying Combined Plumes for OLM ...................................................................... 53 2.6.6 Modeling NO 2 Increment Credits with PVMRM ........................................................ 54 2.7 VARIABLE EMISSION RATES .................................................................................... 60 2.7.1 Specifying Variable Emi ssion Factors (EMISFACT) ................................................. 60 2.7.2 Specifying an Hourly Emissi on Rate File (HOUREMIS) ........................................... 63 2.8 OUTPUT OPTIONS ......................................................................................................... 65 2.8.1 Output Options for 24-hour PM2.5 and 1-hour NO 2 and SO 2 Standards .................... 65v 2.8.2 Miscellaneous Output Options ..................................................................................... 68 2.9 MODEL STORAGE LIMITS ......................................................................................... 70 3.0 REFERENCES ...................................................................................................................... 73 APPENDIX A. ALPHABETICAL KEYWORD REFERENCE ......................................... A-1 APPENDIX B. FUNCTIONAL KEYWORD/PARAMETER REFERENCE ................... B-1 APPENDIX C. LIST OF ERROR/WARNING MESSAGES .............................................. C-1 APPENDIX D. EP A MODEL CLEARINGHOUSE ME MORANDUM DATED JULY 9, 1993 ................................................................................................................. D-1 APPENDIX E. EVALUATION OF MODIFIED URBAN OPTION ................................... E-1 APPENDIX F. EVALUATION OF LOW WIND BETA OPTIONS ................................... F-1vi FIGURES

Figure Page
E-1. 1-hour Q-Q Plot for Indianapol is SF6 Study for All Stabilities ......................................... E-2
E-2. 1-hour Q-Q Plot for Indianapolis SF6 Study for Convective Conditions .......................... E-2
E-3. 1-hour Q-Q Plot for Atlanta NO 2 Study for Monitor 0002 ................................................ E-3
E-4. 1-hour Q-Q Plot for Atlanta NO 2 Study for Monitor 3001 ................................................ E-3
E-5. 1-hour Q-Q Plot for Atlanta NO 2 Study for Monitor 0048 ................................................ E-4
E-6. 1-hour Q-Q Plot for Atlanta NO 2 Study for Monitor JST .................................................. E-4vii TABLES

Table Page
1-1. Summary of Deposition Options in AERMOD .................................................................. 8

B-1. DESCRIPTION OF CONTRO L PATHWAY KEYWORDS ........................................ B-3

B-2. DESCRIPTION OF CONTROL PATH WAY KEYWORDS AND PARAMETERS ... B-5

B-3. DESCRIPTION OF SOURCE PATHWAY KEYWORDS ......................................... B-12

B-4. DESCRIPTION OF SOURCE PATH WAY KEYWORDS AND PARAMETERS .... B-14

B-5. DESCRIPTION OF RECEPTOR PATHWAY KEYWORDS .................................... B-21

B-6. DESCRIPTION OF RECEPTOR PATHWAY KEYWORDS AND PARAMETERS ............................................................................................................ B-22

B-7. DESCRIPTION OF METEOROLO GY PATHWAY KEYWORDS .......................... B-25

B-8. DESCRIPTION OF METEOROLO GY PATHWAY KEYWORDS AND PARAMETERS ............................................................................................................ B-26

B-9. DESCRIPTION OF EVENT PATHWAY KEYWORDS ............................................ B-28

B-10. DESCRIPTION OF EV ENT PATHWAY KEYWORDS AND PARAMETERS....... B-29

B-11. DESCRIPTION OF OUTPUT PATHWAY KEYWORDS ......................................... B-30

B-12. DESCRIPTION OF OUTPUT PATH WAY KEYWORDS AND PARAMETERS .... B-321 1.0 INTRODUCTION

1.1 OVERVIEW OF AERMOD REVISIONS

This document provides user instructions for revisions to the AERMOD dispersion model. The discussion provided here supplements and updates the information contained in the current AERMOD User’s Guide (EPA, 2004a), and it is assumed that the reader is already familiar with the contents of that document. Note that portions of the current AERMOD User’s Guide (EPA, 2004a) are no longe r valid or applicable.

Several sets of AERMOD revisions are included in this Addendum:

1. The first set of revisions, first in troduced with vers ion 03273 of AERMOD, includes dry and wet deposition algorith ms for both particulate and gaseous emissions (see Sections 1.2 and 2.2 for mo re details), and the OPENPIT source option, originally incorporated in the ISCST3 model (EPA, 1995a), for modeling particulate emissions from open pit (below grade) sources, such as surface coal mines and rock quarries;
2. The second set of revisions, first intr oduced with version 04300 of AERMOD, includes two non-DFAULT options for modeling conversion of NO to NO 2 : 1) the Plume Volume Molar Ratio Method (PVMRM) (Hanrahan, 1999a and 1999b); and 2) the Ozone Limiting Method (OLM);
3. The third set of revisions, first intr oduced with vers ion 06341 of AERMOD, includes the following (additional information is provided in Model Change Bulletin (MCB) #1 provided on the SCRAM AERMOD webpage):

a. A new “BETA” option on the CO MODELO PT card to allow for new features to be added to AERMOD that are still in BETA-test status; b. A BETA option for incorporating NO/NO 2 chemistry for NO 2 increment consumption calculations with PSD credits using the PVMRM option;

c. BETA options for capped and horizontal stack releases; d. An option to specify an initial default in-stack NO 2 /NO x ratio for the PVMRM and OLM options;

e. New options for varying emissions by month, hour-of-day, and day-of-week (MHRDOW and MHRDOW7); f. An option to allow multiple urban areas to be defined in a single model run;2 g. Updated processing to support modeli ng demonstrations for the National Ambient Air Quality Standards ( NAAQS) for PM, including the 24-hour average design value for PM-2.5 impacts; and h. Use of dynamic array allocation for AR EAPOLY sources to allocate array limits for the maximum number of verti ces at model runtime, replacing the previous fixed array limit of 20 vertices.
4. The fourth set of revisions, first in troduced with version 09292 of AERMOD, includes the following (additional informa tion is provided in MCB#3 provided on the SCRAM AERMOD webpage):

a. New options for varying emissions by hour-of-day and day-of-week (HRDOW and HRDOW7); b. Modification of the re gulatory default opti on (DFAULT) on the CO MODELOPT card to impose a restric tion on the urban roughness length parameter to be 1 meter for regulatory default applications. Any value other than 1 meter for the urban roughness le ngth option on the CO URBANOPT card will be treated as a non-DFAULT option;

c. Removal of the TOXICS option from the MODELOPT keyword. Options formerly associated with the TOXICS option are still considered non-DFAULT options within AERMOD. The area source optimizations formerly associated with the TOXICS option are now selected using the new non-DFAULT FASTAREA option on the MODELOPT keyword; d. A new non-DFAULT option for optimizing runtime for POINT and VOLUME sources based on an alternative impl ementation of the horizontal meander algorithm has been incorporated through the FASTALL option on the MODELOPT keyword. The FASTALL op tion also includes the FASTAREA optimizations if area sources ar e included in th e model inputs;

e. The option for specifying hourly emissions from a separate file through the HOUREMIS keyword has been enhanced to allow the use of hourly varying release heights and initial disper sion coefficients for VOLUME and AREA/AREAPOLY/AREACIRC sources; f. The OPENPIT source option has been modified to allow for use of the OPENPIT source for gaseous (non-partic ulate) emissions and with METHOD_2 for particulate emissions;

g. The non-DFAULT option of FLAT terrain can now be specified on a source-bysource basis, allowing both FLAT and ELEV terrain treatments within the same model run (see Section 4.1 of the AERMOD Implementation Guide regarding modeling of sources with terrain-fo llowing plumes in sloped terrain); h. A non-DFAULT option for a user-specified dry deposition velocity for gaseous emissions has been added under the GAS DEPVD keyword on the CO pathway; i. A new SUMMFILE option has been incl uded on the OU pathway to output the summary of high ranked valu es to a separate file;3 j. An option to use scientific notation for output result file s has been added through the FILEFORM keyword on the OU pathway. The FILEFORM option is applicable to PLOTFILEs, pl ot-formatted POSTFILEs, MAXIFILEs, RANKFILEs, and SEASONHR files; k. An option (WARNCHKD) has been added to the MODELOPT keyword to allow issuing of warning messages rather than fatal errors for non-sequential meteorological data files, in order to allow use of multi-year meteorological data files that may contain gaps be tween years of data under the DFAULT option; and l. The maximum length of filenames specified in the ‘aermod.inp’ file has been increased to 200 (controlled by the ILEN_F LD parameter in modules.f), and the maximum input string length to 512 (cont rolled by the ISTRG parameter in modules.f). Double quotes (") are also allowed as field delimiters in the 'aermod.inp' file to support filenames with embedded spaces.
5. The fifth set of revisions, first intr oduced with vers ion 11059 of AERMOD, includes the following (additional informa tion is provided in MCB#4 provided on the SCRAM AERMOD webpage):

a. Revisions to the processing options ava ilable for 24-hour averages of PM2.5 to support implementation of recommendati ons regarding appropriate modeling procedures for demonstrating compliance the PM2.5 NAAQS; b. Enhancements to support processing for the 1-hour NO 2 and SO 2 NAAQS, based on the annual distribution of daily maximum 1-hour values, averaged across the number of years processed, in cluding three new output file options, MAXDAILY, MXDYBYYR, and MAXD CONT, and revisions to the RECTABLE keyword to support us er-specified ranks up the 999 th highest value to support significant co ntribution analyses;

c. A new option to specify uniform or temporally-varying background concentrations, using the BACKGRND keyword on the SO pathway; d. A new option to specify temporally-v arying background ozone concentrations, using the O3VALUES keyword on the CO pathway;

e. Incorporation of the default equilibrium ratio 0.90 for NO 2 /NO x for the OLM option, which was previously associated only with the PVMRM option (the CO NO2EQUIL option can also be used to specify a non-default equilibrium ratio for the OLM option); f. Increasing the maximum length for s ource IDs from 8 to 12 characters;

g. An option to suppress file headers fo r formatted output files, using the NOHEADER keyword on the OU pathway; h. A modification to the urban option to address issues w ith the transition from the nighttime urban boundary layer to the daytime convective boundary layer (a non-DFAULT option has been included to allo w users to revert to the original implementation); and4 i. Corrections to several bugs related to the PVMRM algorithm and modifications to the DEBUGOPT keyword to allo w user to specify only PVMRM or deposition (DEPOS) debug output, without the MODEL debug file, which can be very large.
6. The sixth set of revisions, first intr oduced with vers ion 11103 of AERMOD, includes the following (additional informa tion is provided in MCB#5 provided on the SCRAM AERMOD webpage):

a. Correction to a bug that resulted in all short-term values being 0.0 if only the 1st-highest rank was selected for appli cations involving the special processing for daily maximum values (24hr PM25, 1hr NO2 and 1hr SO2); and b. Additional error hand ling to identify potential probl ems with the Fortran format specifier for hourly ozone files and hour ly background files specified on the CO OZONEFIL and SO BACKGRND keywords , respectively. The hourly ozone and/or background concentrations may have been assigned values of zero (0) in previous versions of AERMOD if the user -specified Fortran format included an integer (I) format to read the concentr ation values. The requirements for userspecified Fortran formats with these options has been clarified in the appropriate sections below.
7. The seventh set of revisions, first in troduced with version 12060 of AERMOD, includes the following (additional informa tion is provided in MCB#7 provided on the SCRAM AERMOD webpage):

a. Corrections to bugs associated with the MAXDCONT option for determining source contributions for the 1hr NO 2, 1hr SO2 and 24hr PM25 NAAQS based on a distribution of daily maximum values for applic ations including a day-ofweek component on the EMISFA CT, O3VALUES, or BACKGRND keywords, and for applications us ing an hourly emission file (SO HOUREMIS keyword) for at least one source, but not all sources, in a particular run; b. Corrected a bug for applications with the OLM and PVMRM options under the EVENT processing mode when onl y the CO OZONEVAL keyword is used to specify a background ozone va lue, without an hourly ozone file through the CO OZONEFIL ke yword or varying ozone values through the CO O3VALUES keyword;

c. Replaced subroutine LTOPG for determining PG stability class based on Monin-Obukhov length and surface roughne ss used in the FASTAREA option with code from the CTDMPLUS model that more closely matches the Golder (1972) figure; d. Incorporated an option for users to indicate that all sources in a particular model run are to be treated as URBAN sources, by specifying ‘ALL’ on the SO URBANSRC keyword. The URBANS RC ALL option is only applicable for applications that incl ude a single urban area;5 e. Included a new option for users to specify the number of years of meteorological data being processed for multi-year applications of the MAXDCONT option, using the ne w NUMYEARS keyword on the ME pathway. This allows users with less th an 5 years of site-specific met data to specify the number of years being pro cessed in order to minimize memory storage requirements. Consistent with previous versions, the default number of years absent the NUMYEAR S option is five (5); and f. Includes checks of the range of ranks specified on the OU RECTABLE keyword when the THRESH option on the MAXDCONT keyword is being used, since the analysis of contribu tions for MAXDCONT is limited to the range of ranks specified on the RECTABLE keyword. A fatal error message will be generated if the range of ranks specified is less than or equal to the design value rank for the specified pollutant plus 4, i.e., a fatal error will be generated if the range of ra nks is less than or equal to 8 for 1-hr SO2, or less than or equal to 12 for 1-hr NO2 or 24-hr PM2.5. A non-fatal warning message is also generated if the range of ranks is less than or equal to the design value rank plus 20, i.e., if the range of ranks is less than or equal to 24 for 1-hr SO2, or less than or equa l to 28 for 1-hr NO2 or 24-hr PM2.5.
8. The eighth set of revisions, first in troduced with version 12345 of AERMOD, includes the following (additional informa tion is provided in MCB#8 provided on the SCRAM AERMOD webpage):

a. Adjustments to wind speeds based on the assumption that input wind speeds are vector (or resultant) mean winds (see Eq. 112 on page 79 of the AERMOD Model Formulation Document (Cimorelli, et al. , 2004)) have been removed. This is considered a formulation bug fi x since current EPA guidance for sitespecific meteorological monitoring (EPA , 2000) recommends that scalar mean wind speeds be used in steady-state Gau ssian dispersion models. Furthermore, all wind speeds derived from NWS or F AA airport data represent scalar mean wind speeds. An option has also been included on the MODELOPT keyword on the CO pathway (VECTORWS) that al lows users to specify that input wind speeds are vector means, in which case the previous adjustments will be included. The new VECTORWS option is not linked with the DFAULT option, but users should be able to conf irm that input speeds are vector means in order to justify use of the option. However, scalar mean wind speeds, if available, should be used ba sed on the current guidance. b. Modifications to check for large nega tive hourly emissions (< -90), which may be used as missing indicators. Since AERMOD allows inputs of negative emissions for use in emission credit ca lculations, negative values used as missing indicators in the HOUREMIS file result in negative hourly concentrations in the previous versio ns. Warning messages are generated and the emission rate is set to zero (0) for these cases.

c. Two new BETA (non-Default) options have been included to address concerns regarding model performan ce under low wind speed conditions. The6 LOWWIND1 option increases the minimum value of sigma-v from 0.2 to 0.5 m/s and "turns off" the horizontal meander component. The LOWWIND2 option increases the minimum value of sigma-v from 0.2 to 0.3 m/s, and incorporates the meander component, with some adjustments to the algorithm, including an upper limit on the meande r factor (FRAN) of 0.95. A new LOW_WIND keyword has been added to the CO pathway that allows users to adjust the minimum sigma-v value (with in a range of 0.01 to 1.0 m/s), and the minimum wind speed value (within a range from 0.01 to 1.0 m/s), with a default value of 0.2828 m/s, consistent w ith the default applied in previous versions based on SQRT(2*SVmin*S Vmin) with SVmin=0.2. The new LOW_WIND keyword also allows users to adjust the maximum value for the meander factor (FRAN) within a range of 0.50 to 1.0, inclusive, when the LOWWIND2 option is used. These new LowWind BETA options can also be used in conjunction with the new opt ion in AERMET (v12345) to adjust the surface friction velocity (U*) under lo w-wind/stable conditions (ADJ_U*), based on Qian and Venkatram (2011). More details regarding these LowWind BETA options is provided in Section 2.1.10. d. A new LINE source type has been include d that allows users to specify linetype sources based on a start-point and end-point of the line and the width of the line, as an alternative to the cu rrent AREA source type for rectangular sources. The LINE source type utilizes the same routines as the AREA source type, and will give identical results fo r equivalent source inputs. The LINE source type also includes an optional in itial sigma-z parameter to account for initial dilution of the emissions. As with the AREA source type, the LINE source type does not include the horizont al meander component in AERMOD.

e. Additional range checks on hourly stack ex it velocities and exit temperatures input through the SO HOUREMIS option. A fatal error is generated if the hourly exit temperature is less than 200K (about -100F), unless the hourly emissions are zero (0) for that hour. This may indicate that incorrect units for exit temperature have been used, or that the order of exit temperature and exit velocity may have been reversed in the HOUREMIS file. Also added a new warning message for exit velocities larg er than 250 m/s. Comparable changes were incorporated in subroutine PPARM for inputs on the SRCPARAM keyword. f. Modified the acceptable AERMET version date from 06341 to 11059. AERMOD will no longer run with met data based on version 06341 of AERMET. AERMOD will run using met data based on version 11059. However, a warning message will be generated, and users are strongly encouraged to update their meteorologi cal data to version 12345 of AERMET due to the scope of changes included in that update.

1.2 BACKGROUND ON DEPOSITION ALGORITHMS7 The deposition algorithms incorporated in to AERMOD are based on the draft Argonne National Laboratory (ANL) report (Wesely et al., 2002), with m odifications based on peer review. Treatment of wet deposition was revised from Wesely et al. (2002) based on recommendations by peer review panel memb ers (Walcek et al., 2001). A full technical description of the deposition al gorithms implemented in AERMOD is provided in an EPA report (EPA, 2003).

The deposition algorithms based on the ANL report were initially implemented in the AERMOD model under the non-DFAULT TOXICS op tion, which was selected by including the TOXICS keyword on the CO MODELOPT card. Beginning with ve rsion 09292 of AERMOD, the TOXICS option has been removed from the m odel. Those options in AERMOD that were formerly associated with the TOXICS option are still considered non-DFAULT options but no longer require the specification of the TOXICS option to allow thei r use. The other changes to the AERMOD model inputs associated with th e deposition algorithms are limited to the CO (control) pathway and the SO (source) pathway. For gaseous dry deposition based on the ANL algorithms, the user must define the seasonal cat egories based on the ANL report for each of the calendar months, and must also define the land use category and three pollutant-specific physical parameters that are provided in the appendices of the ANL report. An optional keyword is also provided to override default values for three para meters used in the gas deposition algorithm. The input requirements for “Method 1” particle de position in AERMOD are the same as for the particle deposition algorithm in the ISCST3 mo del and are described below in Section 2.2. For “Method 2” particle deposition, the user must define the fraction of the particle mass in the fine particle category (less than 2.5 microns) and a representati ve mass mean diameter for the particles, which are also provided for selected pollutants in Appendix B of the ANL report. The keywords used to define these inputs and the me teorological data requirements for deposition are
described in Section 2.2.

Consistent with Section 7.2.7(b) of the Guideline on Air Quality Models (40 CFR Part 51, Appendix W), the use of “Method 1” for particle deposition in AERMOD is allowed under the regulatory DFAULT option. However, use of th e “Method 1” particle deposition algorithms require quantification of the par ticle size distribution and should be done in coordination with the8 appropriate reviewing authority. Use of the “Method 2” option for particle deposition and the gas deposition algorithms (both dry and we t) are considered non-DFAULT options in AERMOD. Table 1-1 summarizes the required ke ywords for the various deposition options within AERMOD and whether they are allowed under the DFAULT option.

Table 1-1. Summary of De position Options in AERMOD Pollutant Type Model Output Type Required Keywords Allowed under DFAULT?
Gaseous CONC w/dry depletion DDEP CO GASDEPVD

or CO GDSEASON, CO GDLANUSE, and SO GASDEPOS No

Gaseous CONC w/wet depletion WDEP SO GASDEPOS No

Gaseous CONC w/dry & wet depletion DEPOS CO GDSEASON, CO GDLANUSE, and SO GASDEPOS No

Particulate (“Method 1”) CONC w/dry and/or wet depletion DEPOS DDEP WDEP SO PARTDIAM, SO PARTDENS, and SO MASSFRAX Yes 1

Particulate (“Method 2”) CONC w/dry and/or wet depletion DEPOS DDEP WDEP SO METHOD_2 No

1 While “Method 1” is allowed under the regulatory “DFAU LT” option within AERMOD, the use of “Method 1” for particulate emissions in regulatory modeling applications should follow the guidance provided in Section 7.2.7(b) of Appendix W.9 2.0 USER INSTRUCTIONS

2.1 DISPERSION MODELING OPTIONS

2.1.1 Modification to Urban Option for Morning Transition

The urban option within AERMOD was m odified, beginning with version 11059, to address potential issues associated with the transition from the nighttime urban boundary layer to the daytime convective boundary la yer. Prior to version 11059, the enhanced dispersion due to the urban heat island during ni ghttime stable conditions was i gnored once the rural boundary layer became convective. This could result in an unrealistic drop in the mixing height for urban sources during the morning transition to a conve ctive boundary layer, which could contribute to overly conservative concentrations for low-level sources under such conditions. This potentially
anomalous behavior was observed in a few cases during the applicati on of AERMOD for the Risk and Exposure Assessment (REA) conducted in support of the most recent review for the
NO 2 National Ambient Air Quality Standard (NAAQ S) (EPA, 2008). The pot ential significance of this issue for AERMOD applications in s upport of air quality perm itting has increased with the recent promulgation of the 1-hour NO 2 and 1-hour SO 2 NAAQS.

To address this issue, AERMOD was modifi ed to continue appl ying the urban boundary layer option for urban sources until the daytime (rural) c onvective boundary exceeds the population-dependent urban boundary la yer height. This modificati on to the urban option within AERMOD has been evaluated using the 1985 Indianapolis SF 6 field study data, and shows improved model performance during daytime conv ective conditions compared to the original implementation of the urban option. M odel-to-monitor comparisons of 1-hour NO 2 concentrations from the Atlanta NO 2 REA also exhibit improved model performance with this modification to the urban option in AERMOD. A summary of these model evaluation results is provided in Appendix E.

While the urban option has been modified under the regulatory default mode beginning with version 11059, a non-DFAULT opti on to revert to the urban op tion as implemented prior to10 version 11059 has been included on the CO MOD ELOPT keyword (see Section 2.1.2). As with other non-DFAULT options in AERMOD, use of this option in regulatory modeling applications would require justification and a pproval on a case-by-case basis.

2.1.2 MODELOPT Keyword

The dispersion options are controlled by th e MODELOPT keyword on the CO pathway. The syntax, type, and order of the M ODELOPT keyword are summarized below:

Syntax:

CO MODELOPT DFAULT BETA CONC AREADPLT FLAT NOSTD NOCHKD NOWARN SCREEN SCIM PVMRM PSDCREDIT FASTALL DEPOS and/or or or or DDEP ELEV WARNCHKD OLM FASTAREA and/or WDEP

DRYDPLT WETDPLT NOURBTRAN LOWWIND1 VECTORWS

or or or NODRYDPLT NOWETDPLT LOWWIND2 Type: Mandatory, Non-repeatable Order: Must precede POLLUTID, HALFLIFE and DCAYCOEF

where:

DFAULT - Specifies that the regulatory defa ult options will be used; note that specification of the DFAULT opti on will override some non-DFAULT options that may be specified in the input file, while other nonDFAULT options will cause fatal errors when DFAULT is specified (see below for details);

BETA - Non-DFAULT option that allows for draft, “Beta” test options to be used (see Section 2.1.3 for more de tails); currently includes the PSDCREDIT option (Section 2.5.6); op tions for capped and horizontal stack releases (2.1.9); the LOWWI ND1 and LOWWIND2 options and the use of meteorological inputs based on the non-Default ADJ_U* option incorporated in version 12345 of AERMET that adjusts the surface friction velocity (U*) under low-wind/stable conditions (Section 2.1.10),;

CONC - Specifies that concentration values will be calculated;11 DEPOS - Specifies that total deposition flux values (both dry and wet) will be calculated;

DDEP - Specifies that dry deposition fl ux values will be calculated;

WDEP - Specifies that wet deposition fl ux values will be calculated;

AREADPLT - Specifies that a non-DFAULT met hod for optimized plume depletion due to dry removal mechanisms will be included in calculations for area sources;

FLAT - Specifies that the non-DFAULT opt ion of assuming flat terrain will be used; Note that FLAT and ELEV ma y be specified in the same model run to allow specifying the non- DFAULT FLAT terr ain option on a source-by-source basis; FLAT sour ces are identified by specifying the keyword FLAT in place of the source elevation field on the SO LOCATION keyword;

ELEV - Specifies that the default option of assuming elevated terrain will be used; Note that FLAT and ELEV ma y be specified in the same model run to allow specifying the non- DFAULT FLAT terr ain option on a source-by-source basis;

NOSTD - Specifies that the non-DFAULT option of no stack-tip downwash will be used;

NOCHKD - Specifies that the non-DFAULT option of suspending date checking will be used for non-sequential meteorological data files;

WARNCHKD - Specifies that the option of issu ing warning messages rather than fatal errors will be used for non-sequent ial meteorological data files;

NOWARN - Specifies that the option of suppr essing the detailed listing of warning messages in the main output file will be used (the nu mber of warning messages is still reported, and warn ing messages are still included in the error file controlled by the CO ERRORFIL keyword);

SCREEN - Specifies that the non-DFAU LT option for running AERMOD in a screening mode will be used;

SCIM - Sampled Chronological Input Model - used only with the ANNUAL average option to reduce runtime by sampling meteorology at a userspecified regular inte rval; SCIM sampling parameters must be specified on the ME pathway;12 PVMRM - Specifies that the non-DFAU LT Plume Volume Molar Ratio Method (PVMRM) for NO 2 conversion will be used;

OLM - Specifies that the non-DFAU LT Ozone Limiting Method (OLM) for NO 2 conversion will be used;

PSDCREDIT - Specifies that the non-DFAULT BE TA test option will be used to calculate the increment consumption with PSD credits using the PVMRM option;

FASTALL - Non-DFAULT option to optimi ze model runtime through use of alternative implementation of hor izontal meander for POINT and VOLUME sources; also optimizes model runtime for AREA/ AREAPOLY/AREACIRC and OPEN PIT sources through hybrid approach (formerly associated wi th TOXICS option, now controlled by FASTAREA option);

FASTAREA - Non-DFAULT option to optimi ze model runtime through hybrid approach for AREA/ AREAPOLY/AREACIRC and OPENPIT sources (formerly associated with TOXICS option);

DRYDPLT - Option to incorporate dry deplet ion (removal) processes associated with dry deposition algorithms; th is requires specification of dry deposition source parameters and additional meteorological variables; dry depletion will be used by default if dry deposition algorithms are invoked;

NODRYDPLT - Option to disable dry depletion (r emoval) processes associated with dry deposition algorithms;

WETDPLT - Option to incorporate wet deple tion (removal) pro cesses associated with wet deposition algorithms; this requires specification of wet deposition source parameters and additional meteorological variables; wet depletion will be used by default if wet deposition algorithms are invoked;

NOWETDPLT - Option to disable wet depletion (r emoval) processes associated with wet deposition algorithms;

NOURBTRAN - Non-DFAULT option to ignore th e transition from nighttime urban boundary layer to daytime convective boundary layer (i.e., to revert to the urban option as implemented prior to version 11059);

LOWWIND1 - Non-DFAULT BETA option to a ddress concerns regarding model performance under low wind speed conditions. The LOWWIND1 option increases the minimum valu e of sigma-v from 0.2 m/s to 0.513 m/s, and “turns off” the horizontal meander component. The BETA keyword must also be specified in order to invoke the LOWWIND1 option;

LOWWIND2 - Non-DFAULT BETA option to a ddress concerns regarding model performance under low wind speed conditions. The LOWWIND2 option increases the minimum valu e of sigma-v from 0.2 m/s to 0.3 m/s, and includes some adjustme nts to the horizontal meander component. The BETA keyword must also be specified in order to invoke the LOWWIND2 option (note that LOWWIND1 and LOWWIND2 cannot both be invoked in the same model run);

VECTORWS - Option to specify that input wind sp eeds are vector mean (or resultant) wind speeds, rather than scalar means. Under the VECTORWS option, the adjustments to wind spee ds based on Equation 112 of the AERMOD Model Formulati on Document (Cimorelli, et al. , 2004) will be applied. The VECTORWS option is not linked with the DFAULT option.

The DFAULT option has been modified beginni ng with version 09292 to impose a restriction on the optional urban roughness length parameter to be 1 meter for regul atory default applications.

The user may select any or all of the output types (CONC, DEPOS, DDEP and/or WDEP) to be generated in a single model run. The order of these secondary keywords on the
MODELOPT card has no effect on the order of results in the output files - the outputs will always be listed in the order of CONC, DE POS, DDEP, and WDEP. Appropriate deposition parameters must be specified in order to ou tput deposition fluxes using the DEPOS, DDEP, and/or WDEP keywords (see Sectio ns 1.2 and 2.2 for more details).

Beginning with version 04300, the dry and/or we t removal (depletion) mechanisms (the DRYDPLT and WETDPLT options in earlier vers ions of AERMOD) will automatically be
included in the calculated concentrations or deposition flux values if the dry and/or wet deposition processes are considered, unless the user specifies the NODRYDPLT and/or NOWETDPLT options. Note that dry and wet removal effect s on calculated concentration values can be included even if deposition flux va lues are not being calculated. However, the additional data requirements for dry and wet deposition, described in Section 2.2, must be met in order for dry and wet removal to be included in the concentration calculat ions. The use of the14 NODRYDPLT and/or NOWETD PLT options will result in a mo re conservative estimate of concentrations and/or deposition fluxes for appl ications involving depositi on processes, but the degree of additional conservatism will vary depending on the source characteristics, meteorological conditions, receptor locations and te rrain influences. However, the inclusion of particle deposition effects may increase ground-level concentrati ons for some sources compared to the same source modeled as a gaseous emissi on, due to the effect of gravitational settling on the particulate plume. The magnitude of this effect will depend on th e source characteristics (elevated or low-level) a nd particle size distribution.

The PVMRM and OLM options for modeling NO 2 conversion are non-DFAULT options, and only one of these options can be specified fo r a given model run. Both options require that the pollutant ID be specified as ‘NO2’ on the CO POLLUTID card (see Section 3.2.5 of the
AERMOD User = s Guide). These options have additiona l input requirements as described in
Section 2.6.

Beginning with version 09292, the TOXICS op tion in no longer used in AERMOD and the FASTAREA option on the MODELOPT is now used to select the non-DFAULT option to optimize model runtime for AREA sources (including AREA, AREA POLY, AREACIRC and OPENPIT source types, as well as LINE sour ces introduced with version 12345 (see Section X.X)). When the FASTAREA option is spec ified, the area source integration routine is optimized to reduce model runtime by incorporat ion of a three-tiered approach using the Romberg numerical integration, a 2-point Gaussian Quadrature routine for numerical integration, or a point source approximation, depending on the loca tion of the receptor rela tive to the source. In the regulatory default mode the Romberg numerical integration is utilized for all receptors. Also beginning with version 09292, a non-DFAU LT option to optimize model runtime for POINT and VOLUME sources has been included, which is selected by the FASTALL option on the MODELOPT keyword. Specification of the FASTALL option also activates the FASTAREA option if AREA sources are includi ng in the model inputs. Both FASTALL and FASTAREA skip receptors that are more than 80 kilometers from the source.15 The FASTALL option for POINT and VOLUME sources uses an alternative implementation of the horizontal meander algor ithm based on an effective horizontal dispersion coefficient ( σ yeff ) that replicates the centerline concentr ation based on the full meander approach.
Use of the effective σ y allows the model runtime to be optimized by skipping receptors that are
more than 4 σ yeff off the plume centerline. Based on te sts conducted to da te, comparisons of concentrations based on the FASTALL op tion for POINT and VOLUME sources with concentrations based on the DFAULT option are si milar to comparisons of concentrations for AREA sources using the FASTAREA option. The average ratio of FASTALL concentrations to DFAULT values is about 1.02 for high ranked values, showing a slight bias toward overprediction for the FASTALL option. However, the range of ratios fo r high ranked values shows both overpredictions and underpredictions relative the DFAULT option, and differences at specific receptors may be much larger.

The NOURBTRAN non-DFAULT option has been included to allow users to revert to the urban option as implemented prior to vers ion 11059, which ignores the transition from the nighttime urban boundary layer to the daytime c onvective boundary layer. As with other nonDFAULT options in AERMOD, use of the NOURBTRAN option in regulatory modeling applications would require justificati on and approval on a case-by-case basis.

2.1.3 BETA Test Options

A 'BETA' test option switch is included on the CO MODELOPT keyword to identify and
allow for new features to be added to the model that are still in a draft BETA-test status. The BETA option is a non-DFAULT option, and will result in a fatal error if the DFAULT option is also specified. Draft enhancements include d in AERMOD under the BETA option, through version 12345, include:

1) Options for capped stacks (source type = POINTCAP) and for horizontal releases (source type = POINTHOR);
2) The PSDCREDIT option for PVMRM to account for NO/NO 2 chemistry of combined plumes in the computation of increment consumption with PSD credits;16 3) The LOWWIND1 and LO WWIND2 options under the CO MODELOPT keyword to address concerns regarding model performance under low wind speed conditions; and
4) The ADJ_U* option incorporated in version 12345 of AERMET that adjusts the surface friction velocity (U*) under low wi nd/stable conditions (see AERMET User’s Guide Addendum for more detail s regarding the ADJ_U* option).

Inclusion of these draft BETA-t est options does not imply any endorsement of their use for regulatory or non-regulatory applic ations of the model. In add ition, the designation of BETA-test to these draft enhancements does not imply that these options have completed rigorous internal (“Alpha”) testing prior to being in cluded in a public rele ase of the model. More details regarding the POINTCAP and POINTHOR options are provid ed in Section 2.1.9; more details regarding the PSDCREDIT option are provided in Sect ion 2.5.6; and more details regarding the LOWWIND1 and LOWWIND2 options in AERMOD and the ADJ_U* option in AERMET are provided in Section 2.1.10.

2.1.4 Averaging Time Options

The averaging periods for AERMOD are se lected using the AVERTIME keyword on the CO (Control) pathway. The syntax and type of the AVERTIME keyword are summarized below:

Syntax: CO AVERTIME Time1 Time2 . . . TimeN MONTH PERIOD

or ANNUAL Type: Mandatory, Non-repeatable

where the parameters Time1 . . . TimeN refer to the user-specified short term averaging periods
of 1 , 2 , 3 , 4 , 6 , 8 , 12 , and/or 24 hours, the secondary keyword MONTH refers to monthly averages (for calendar months), the secondary keyword PERIOD refers to the average for the entire data period, and th e secondary keyword ANNUAL refers to an annual average. Any of the short term averaging periods listed above may be selected for a given run. Since the monthly averages are treated as short term averages, the user can select appropriate output options, such as the second highest values by receptor, on the OU pathway. The location of the PERIOD or17 ANNUAL keyword in the parameter list is not critic al. The order of the short term averaging periods (including MONTH ) is also not critical, although it does control the order of the averaging period result tables in the main output file. Generally, it is recommended that the short term averaging periods be input in increasing or der, unless there is a clear advantage in doing
otherwise.

The user may specify either the PERIOD keyword or the ANNUAL keyword, but not both. For concentration calculations, the PERIOD and ANNUAL keywords produce the same results for a single year data file. However, the ANNUAL average option applies only to complete years of data, and fo r multi-year data files, the ANNUAL average output is based on the average of the ANNUAL values across the years of da ta processed. For deposition calculations, the PERIOD keyword will provide a total deposition flux for the full period of meteorological data that is mode led, including multi-year data file s, with default units of g/m 2

, whereas the ANNUAL keyword will provide an annualized rate of th e deposition flux with default units of g/m 2 /yr. Use of the ANNUAL average option for meteor ological data periods of less than a year will resu lt in a fatal error. For meteorologica l data periods of longer than a year, if the meteorological data file does not contain co mplete years of data, any data remaining after the last complete year will be ignored for the ANNUAL average, and a warning message will be generated. The treatment of short term averages with multiple-year data files is comparable to
their treatment when the CO MULTYEAR option is used (see Section 2.1.5 below for a description of the MULTYEAR option).

2.1.5 Performing Multiple Year An alyses with MULTYEAR Option

The MULTYEAR keyword on the CO pathwa y provides an option for the user to perform a multiple year analysis such as would be needed to determine the "high-sixth-high in five years" design value for determining PM- 10 impacts without the need for postprocessing of multiple concentration files, and for multiple ye ar analyses associated with the 24-hour PM2.5 NAAQS and 1-hour NO 2 and SO 2 NAAQS which are based on con centrations averaged across the number of years processed. More inform ation regarding the 24-hour PM2.5 and 1-hour NO 2 and SO 2 NAAQS is provided in Sections 2.1.6 and 2.1.7. Since the multiple year option makes18 use of the model re-start capab ilities described in the Sect ion 3.2.10 of the AERMOD User’s Guide (2004a), the MULTYEAR keyword is not compatible with the SAVEFILE or INITFILE keywords. The model will generate a fatal error me ssage if the user attempts to exercise both options in a single run. The syntax and type of the MULTYEAR keyword is summarized below:

Syntax: CO MULTYEAR (H6H ) Savfil (Inifil) Type: Optional, Non-repeatable

where the optional H6H field, formerly used to highlight the use of the MULTYEAR option for determining the High-6 th -High (H6H) 24-hour average for the “pre-1997” PM-10 NAAQS, is no longer required since the “post-1997” PM-10 NAAQS was vacated. A warning message will be generated if the H6H field is included on the MULTYEAR ke yword indicating that it is not required. The Savfil parameter specifies the filena me for saving the results arrays at the end of each year of processing, and the Inifil parameter sp ecifies the filename to use for initializing the results arrays at the beginning of the current year . The Inifil parameter is optional, and should be left blank for the first year in the multi-year series of runs. The MULTYEAR option works by accumulating the high short term average results from year to year through the mechanism of the re-start save file. The model may be setup to run in a batch file with several years of meteorological data, and at the end of each year of processing, the short term average results reflect the cumulative high values for the years th at have been processed. The PERIOD average results are given for only the current year, but th e model carries the highe st PERIOD values from year to year and includes the cumulative highest PERIOD averages in th e summary table at the
end of the run.

When setting up a batch file to perform a multiple year analysis, the user would first create an input runstream file for the first year with all of the appli cable modeling options, the source inventory data, the receptor locations, the meteorology options for the first year and the output file options. To obtain the PM-10 design value, be sure to include the SIXTH highest value on the OU RECTABLE card (see Section 3.7.1 of the AERMOD User’s Guide (2004a)). For the CO MULTYEAR card for the first year , the user would only specify the Savfil parameter, and may use a card such as:19 CO MULTYEAR YEAR1.SAV

For the subsequent years, the user could copy the input file created for Ye ar-1, and edit the files to change the year parameters and meteorology f ilename on the ME pathway (and possibly in the title information), and edit the MULTYEAR cards. For the subsequent years, both the Savfil and Inifil parameters must be specified, with the Savfil for Year-1 becoming the Inifil for Year-2, and so on. The MULTYEAR cards (one for each AERMOD run) might look like this:

CO MULTYEAR YEAR1.SAV (First year) CO MULTYEAR YEAR2.SAV YEAR1.SAV (Second year) CO MULTYEAR YEAR3.SAV YEAR2.SAV (Third year) CO MULTYEAR YEAR4.SAV YEAR3.SAV (Fourth year) CO MULTYEAR YEAR5.SAV YEAR4.SAV (Fifth year)

The MULTYEAR keyword option is separate from the ability of the AERMOD model to process a multiple-year meteorological data file in a single model run. The latter capability can be used for applications of the model to long term ri sk assessments where the average impacts over a long time period are of concern rather than the maximum annual average determined from five individual years.

2.1.6 Processing for Particulate Matter (PM) NAAQS

2.1.6.1 Processing for Fine Pa rticulate Matter (PM-2.5)

A NAAQS for fine particulate matter, with aerodynamic particle diameters of 2.5 microns or less (PM-2.5), was promulgated in 1997, and the 24-hour standard was revised in December 2006. For attainment demonstrations, the PM-2.5 standard is based on a 3-year average of the 98 th percentile 24-hour average and a 3-year average of the annual mean
concentration at each ambient monitor. EPA has issued recommendations (EPA, 2010a) regarding appropriate modeling procedures for use in modeling demonstrations of compliance with the PM2.5 NAAQS, which include a recommendati on to use the average of the first-highest 24-hour average concentrations across the numbe r of years modeled to represent the modeled20 contribution for a cumulative impact assessmen t, as well as for si gnificant contribution determinations. Note that the use of a 3-year average for monitored design values to determine attainment of the NAAQS does not preempt the requirement in Section 8.3.1.2 of the Guideline on Air Quality Models (40 CFR Part 51, Appendix W) for us e of 5 years of National Weather Service (NWS) data, and the 5-year average of m odeled impacts serves as an unbiased estimate of the 3-year average for purposes of modeling de monstrations of compliance with the NAAQS.

Based on these EPA recommendations, the 24- hour modeled contribution to the design value for purposes of modeling demonstrations of compliance with the PM-2.5 NAAQS is based on the highest of the first-highest (H1H) concentra tions at each receptor, if one year of sitespecific meteorological data is input to the model, or the highest of the multi-year average of the first-highest concentrations at ea ch receptor, if more than one y ear of meteorological data is input to the model. In other words, the model calculates the first-highest 24-hour concentration at each receptor for each year modeled, averages those first-highest concentrations at each receptor across the number of year s of meteorological data, and th en selects the highest, across all receptors, of the N-year averaged first-highest values.

Similar to the 24-hour averages, an unbiased estimate of th e 3-year average annual mean is simply the annual mean, if only one year of s ite-specific meteorological data is input to the model, or the multi-year average of the annual m eans if multiple years of meteorological data are used. The annual design value for PM-2.5 is th en based on the highest annual average across the receptor domain for single-year meteorological data input, or the highest of the multi-year averaged annual means across the receptor domai n for multi-year meteorological data input.

The special processing of the 24-hour and a nnual averages for the PM-2.5 NAAQS is triggered by specifying a pollutant ID of ‘PM 25’, ‘PM-2.5’, ‘PM2.5’ or ‘PM-25’ on the CO POLLUTID card. In this case, the model will compute the 24-hour and annual average design values as described in the previous paragraphs . In order for the PM-2.5 processing to work correctly for multiple year periods, the yearly meteorological data files can be concatenated into a single multi-year file for input into the m odel, or the MULTYEAR option (Section 2.1.5) can be used with separate model runs for each year. There is no requirement to remove the header21 records between concatenated surface meteorological data files prior to running the model, and multi-year meteorological data f iles can also be generated by processing multi-year inputs in AERMET, the meteorological processor for AERMOD. (NOTE: While the MULTYEAR option with separate yearly meteorological data files can be used to determine the modeled design values for PM2.5, the OU MAXDCONT option (see Section 2.8.1) to determine contributions from other source groups to the cumulative modeled design value will not work with the MULTYEAR option or with separate meteorological data files for each year.) Processing the average of the individual annua l mean values across multiple years for PM-2.5 also requires use of the ANNUAL average option on the AVERTIME keyword, rather than PERIOD average. The PERIOD op tion computes a single multi-year average concentration for each receptor, which may give slightly different re sults than the multi-year average of individual
ANNUAL mean concentrations due to differences in the number of calms and/or missing data from year to year.

In order to comply with these processing requirements, the following restrictions are applied to the PM-2.5 NAAQS processing whenever a pollutant ID of ‘PM25’, ‘PM-2.5’ or ‘PM-25’ is specified on the CO POLLUTID keyword:

1. The averaging periods on the AVERTIME keyword are limited to the 24-hour and ANNUAL averages. Use of the PERIOD average or use of a short-term average other than 24-hour will result in a fatal error message being generated.

2. The FIRST (or 1ST) highest value should be requested on the RE CTABLE keyword for 24-hour averages for estimating modeled PM 2.5 contributions for compliance with the NAAQS. However, the model places no re striction on the ranks requested on the RECTABLE keyword since sele ction of ranks lower than the FIRST highest may be needed to determine whether a source or gr oup of sources is contri buting significantly to modeled violations of the NAAQS.

3. The model will only process meteorological data for periods of record that span complete years, although the meteorological data peri od does not need to follow calendar years (i.e., the data period does not need to start on January 1, hour 1). If the period of record spans less than one complete year of data, a fatal error message will be generated and the model run will be unsuccessful. If additional meteorological data remains after the end of the last complete year of data, the remainin g data will be ignored, and a non-fatal warning message will be generated specifying the number of hours ignored.22 4. The MULTYEAR keyword on the CO pathway can be used to calculate multi-year averages for the PM-2.5 NAAQS; however , the MAXDCONT option will not work with the MULTYEAR. Multiple year analyses are best accomplished by including the multiple years of meteorol ogy in a single data file.

5. Since the 24-hour average design values for PM-2.5 analyses, based on the H1H averaged over N years, may consist of aver ages over a multi-year period, they are not compatible with the EVENT processor, and the high ranked values generated based on the RECTABLE keyword will not be included in the EVENTFIL. However, if the MAXIFILE option is used to output 24- hour averages exceeding a user-defined threshold, these individual exceedances ma y be used with the EVENT processor. Therefore, if the EVENTFIL option is us ed without the MAXIFILE option for PM-2.5 analyses, a non-fatal warning message will be generated, and the EVENTFIL option will be ignored.

2.1.6.2 Processing for Particulate Matte r of 10 Microns or Less (PM-10)

The 24-hour NAAQS for particulate matter w ith aerodynamic particle diameters of 10 microns or less (PM-10) is in the form of an expected exceedance value, which cannot be exceeded more than once per year on average ov er a three year period for purposes of monitored attainment demonstrations. Modeling demonstr ations of compliance with the PM-10 NAAQS are based on the High-N+1-High value over N year s, or in the case of five years of NWS meteorological data, the High-6 th -High (H6H) value over five year s. In the AERMOD model, the H6H 24-hour average over five years can be m odeled in one of two ways: 1) running five individual years and combini ng the results using the CO MULTYEAR option, as described above in Section 2.1.5; or 2) usi ng a single five-year meteorological data file and specifying the SIXTH (or 6TH) highest valu e on the OU RECTABLE card. If applied properly, the 24-hour average results of these two approaches will be equivalent. The special processing consisting of
the 99 th percentile 24-hour value averaged over N years for PM-10 in versions of AERMOD prior to 09292, referred to as the “Post-1997” PM-10 option, has been removed since that
standard was vacated.

2.1.7 Processing for 1-hour NO 2 and SO 2 NAAQS23 New 1-hour NAAQS for NO 2 and SO 2 were promulgated in February 2010 and June 2010, respectively. EPA has issued guidance relate d to dispersion modeling in support of these 1-hour standards (EPA, 2010b; EPA, 2010c; and EP A, 2011). The form of these new 1-hour standards is similar, based on a percentile rank from the annual distribution of daily maximum 1- hour values, averaged across the number of years processed. For the 1-hour NO 2 standard the modeled design value is based on the 98 th -percentile of the daily ma ximum 1-hour values, which is represented by the eighth-highest of the daily maximum 1-hour values across the year. The 1-
hour SO 2 modeled design value is based on the 99 th -percentile, or fourth-highest, of the daily maximum 1-hour values across the year. For typical multi-year modeling analysis based on 5 years of NWS meteorological data, the modeled de sign value is the 5-year average of the eighthhighest values daily maxi mum 1-hour values for NO 2 , or fourth-highest values for SO 2 .

The form of these new 1-hour standards co mplicates the process of determining the modeled design value as well as the analyses that may be required to determine whether a particular source or group of s ources contributes significantly to any modeled violations of the standards, paired in time and space. Severa l enhancements have been incorporated into AERMOD, beginning with version 11059, to faci litate the modeling anal yses required to demonstrate compliance with these new standards. These enhancements are described in Section 2.8.1. The ability of the model to exercise these new options is facilitated by specifying ‘NO2’ or ‘SO2’ as the pollutant ID on the CO POLLUT ID keyword, with the following restrictions. Whenever a pollutant ID of ‘NO2’ or ‘SO2’ is specified and 1-hour aver ages are selected, the options to calculate 1-hour NO 2 or SO 2 design values based on the distribution of daily maximum 1-hour values will be allowed, unless s hort-term averaging periods other than 1-hour are also specified on the AVERTIME keyword. Ifother short-term averages are specified, nonfatal warning messages will be generated and the options for processing 1-hour NO 2 or SO 2 design values will be disabled. In that case, the 1-hour modeled design values will be processed the same as other short-term averages, based on th e overall distribution of hour ly values. Also, if ANNUAL or PERIOD averages are specified on the AVERTIM E keyword along with 1-hour averages, a non-fatal warning message will be generated unless the CO MULTYEAR keyword is specified, since the annual NAAQS for NO 2 and SO 2 is based on the highest PERIOD or ANNUAL average from an individual year, rather than an average across the years modeled.24 However, the special processing based on daily ma ximum1-hour values will be still applied for the 1-hour averages in these cases since the ANNUAL or PERIOD averages may be appropriate if only 1 year of site-specific meteorological data is modeled.

2.1.8 Specifying Multiple Urban Areas

The AERMOD model (beginning with the vers ion dated 06341) includes the option to specify multiple urban areas within the same model run. This option may be applicable for large domains that encompass more than one identifi able urban area where the separation is large enough to warrant separate treatment of the urba n boundary layer effects. Use of the option for multiple urban areas eliminates the need for post-processing for such applications. The multiple urban areas are defined using multiple CO URB ANOPT cards. The syntax of the modified URBANOPT keyword is as follows:

Syntax: For Multiple Urban Areas: CO URBANOPT UrbanID UrbP op (UrbName) (UrbRoughness)

For Single Urban Areas: CO URBANOPT UrbPop (UrbName) (UrbRoughness) Type: Optional, Repeatable for multiple urban areas

where the UrbanID parameter is the alphanumeric urban ID defined by the user (up to eight characters) when multiple urban areas are defined, the UrbPop parameter specifies the population of the urban area, the optional UrbName parameter may be used to identify the name of the urban area, and the op tional UrbRoughness parameter may be used to specify the urban surface roughness length. Note the UrbName must be specified if the user wants to specify the urban roughness length. A default value of 1.0 meter will be used for the urban roughness length if the UrbRoughness parameter is omitted. Beginning with version 09292, any value for the urban roughness length other than 1.0 meter will be treated as a non-DFAULT option. Caution should be used when specifying a non-defau lt urban roughness length, an d use of a non-default value should be clearly documented and justif ied. Note that the s yntax of the URBANOPT25 keyword for single urban areas ha s not changed from the previous version of AERMOD, so that existing input files will not require modification.

The syntax of the URBANSRC keyword on the SO pathway has also been modified to allow for the option of specifying multiple urban areas. The syntax of the modified URBANSRC keyword is as follows:

Syntax: For Multiple Urban Areas: SO URBANSRC UrbanID SrcID’s and/or SrcRng’s

For Single Urban Areas: SO URBANSRC SrcID’s and/or SrcRng’s

or SO URBANSRC ALL (to specify all sources as URBAN) Type: Optional, Repeatable Order: Must follow the LOCATION card for each source input

where the UrbanID parameter is the alphanumeric urban ID (up to eight characters) defined by the user on the CO URBANOPT keyword when multiple urban areas are defined, and the SrcID's and SrcRng's are the individual source IDs and/or source ID ra nges that are to be modeled with urban effects. Source ranges are de scribed in more detail in Section 3.3.3 of the AERMOD User’s Guide (EPA, 2004a). As with the URBANOPT keyword, the syntax of the URBANSRC keyword for applicat ions with single urban area s has not changed from the previous version of AERMOD, so that exis ting input files will not require modification. However, beginning with version 12060, users can sp ecify that all sources are to be treated as urban sources by specifying ‘ALL’ on the SO U RBANSRC keyword for a pplications with a single urban area. Since the URBANSRC ALL option is identifie d during the pre-SETUP phase,
there are no restrictions on the order of the URBANSRC ALL ke yword within the SO pathway.

2.1.9 BETA Options for Capped and Horizontal Stack Releases

Draft BETA test options are included in AERMOD (beginning with the version dated 06341) for modeling releases from capped and horizont al stacks. For source s that are not subject26 to building downwash influences, the plume ri se for these capped and horizontal stacks is simulated based on an EPA Model Clearinghouse Memorandum, dated July 9, 1993, included in Appendix A of this Addendum. The Model Clea ringhouse procedure for these sources entails setting the exit velocity very low (0.001 m/s) to account for s uppression of vertical momentum for the plume, and using an effective stack diamet er that maintains the actual flow rate of the plume. Maintaining the flow rate will also se rve to maintain the buoyanc y of the plume in order to provide a more realistic estimate of plum e rise. The Model Clearinghouse procedure also
addresses the issue of stack-t ip downwash for these cases.

The Model Clearinghouse procedure is not cons idered appropriate for sources subject to building downwash influences with the PRIME downwash algorithm for the following reason. The PRIME algorithm uses the specified stack diamet er to define the initial radius of the plume for the numerical plume rise calculation; use of an effective diameter adjusted to maintain flow rate is not appropriate and c ould produce unrealis tic results. For PRIME downwash sources modeled using the BETA options for capped and horizontal releases, the basic premise of the Model Clearinghouse procedure, i.e. that the vertical momentum is suppressed while the buoyancy of the plume is conserved, have been adapted for the PRIME numerical plume rise formulation. However, this adaptation of the Model Clearinghouse procedure to PRIME
downwash sources has not been validated by field tracer or wind tunnel data.

The user selects the BETA options for cappe d and/or horizontal re leases by specifying one of the new source types on the SO LOCATI ON card: POINTCAP for capped stacks, and
POINTHOR for horizontal releases. For each of th ese options, the user specifies the actual stack parameters [release height (m), exit temperature (K ), exit velocity (m/s), and stack diameter (m)] using the SO SRCPARAM card as if the release were a non-capped vertical point source. The syntax of the SO LOCATION and SRCPARAM ke ywords is described in Sections 3.3.1 and 3.3.2, respectively, of the AERMOD User’s Guid e (EPA, 2004a), and is also summarized in Appendix B of this Addendum. The AERMOD model performs the necessary adjustments internally to account for plume rise and stack-tip downwash. Fo r horizontal releases, the model currently assumes that the rel ease is oriented with the wind direction, and the model does not
account for directional eff ects that may occur with horizontal releases. The model also does not27 account for stacks oriented at a non-horizontal angl e relative to vertical. For PRIMEdownwashed sources, the user-specified exit velocity for horizontal re leases is treated initially as
horizontal momentum in the downw ind direction. More details regarding the BETA options for capped and horizontal releases wi ll be provided later, as warran ted based on further testing and
evaluation.

2.1.10 BETA Options for Low Wind Conditions

Draft BETA test options are included in AERMOD (beginning with the version dated 12345) for addressing concerns regarding mode l performance under low wind speed conditions, including the LOWWIND1 and LOWWIND2 options on the MODELOPT keyword. The LOWWIND1 BETA option increases the minimum value of sigma-v from 0.2 to 0.5 m/s and "turns off" the horizontal meander component . The LOWWIND2 BETA option increases the minimum value of sigma-v from 0.2 to 0.3 m/s, but incorporates the meander component with some adjustments. Under the LOWWIND2 option an upper limit of 0.95 is applied to the meander factor (FRAN). The LOWWIND1 and LOWWIND2 BETA options are mutually exclusive and the model will issue a fatal warning message if both options are specified.

Although the LOWWIND1 and LOWWIND2 BETA options incorporate preset values for the minimum sigma-v, and in the case of LOWWIND2 the maximum meander factor, consistent with the developmental nature and the BETA status of these options, a LOW_WIND keyword has been added to the CO pathway that allows users to adjust the minimum sigma-v value (SVmin) for both LowWind options (withi n a range of 0.01 to 1.0 m/s), and the minimum wind speed value (WSmin), within a range from 0.01 to 1.0 m/s. Inclusion of the LOW_WIND keyword is intended to facilitate further testi ng and evaluation of the Lo wWind options. Absent user-specified values on the LOW_WIND keywor d, a default value of 0.2828 m/s is used for WSmin, consistent with the default applied in previous versions of AERMOD based on SQRT(2*SVmin*SVmin) with SVmin=0.2. The LO W_WIND keyword also allows users to adjust the maximum value for the meander fact or (FRANmax), within a range of 0.50 to 1.0, inclusive, when the LOWWIND2 option is used. The syntax and type of the LOW_WIND keyword are:28 Syntax: CO LOW_WIND SVmin (WSmin) [for LOWWIND1] CO LOW_WIND SVmin (WSmin (FRANmax)) [for LOWWIND2] Type: Optional, Non-repeatable

where SVmin is the minimum value of sigma-v, w ithin a range of 0.01 to 1.0 m/s, WSmin is the minimum wind speed, within a range of 0.01 to 1.0 m/s, and FRANmax is the maximum meander factor under the LOWWIND2 option, with in a range of 0.50 to 1.0, inclusive. The WSmin parameter on the LOW_WIND keyword is optional for both LowWind options, and the FRANmax parameter is also optional for the LO WWIND2 option. However, a value for WSmin
must also be included in order to specify a value for FRANmax.

In addition to the adjustments to SVmin and meander described above, both of the LowWind BETA options also modify the adjustme nt of vector mean wind speeds (based on Eq. 112, p. 79, of the AERMOD Model Formulation Document (Cimorelli, et al. , 2004)) to use the original values of sigma-v based on Secti on 4.1.6 of the AERMOD MFD, before they are adjusted based on SVmin.

In addition to the LowWind BETA options, an option has been incorporated in the AERMET meteorological processo r (beginning with the version dated 12345) to address concerns regarding model performance under low wind conditions. The ADJ_U* option in AERMET, which adjusts the surface friction ve locity (U*) under low-wind/stable conditions based on Qian and Venkatram (2011), can be used with or without the LOWWIND1 and LOWWIND2 options. However, use of meteor ological data based on the ADJ_U* option requires that the BETA option be specified on the MODELOPT keyword even if the BETA LowWind options are not used since the ADJ_U* op tion is also considered a non-Default option. See the AERMET Model Change Bulletin (MCB) #3 and AERMET User's Guide Addendum for additional details regarding th e ADJ_U* option in AERMET.

As noted above, the LowWind BETA opti ons in AERMOD and the ADJ_U* option in AERMET are considered to be non-Default options and are therefore subject to the alternative29 model provisions in Section 3.2 of Appendix W ( 40 CFR Part 51). Users should coordinate with the appropriate reviewing author ity regarding the procedures a nd requirements for approval of these BETA options for regulat ory modeling applications. A ppendix F provides a summary of preliminary evaluations of the LowWind BETA options in AERMOD in conjunction with the ADJ_U* option in AERMET.

2.2 DEPOSITION ALGORITHM INPUTS AND OPTIONS

The AERMOD model includes algorithms fo r both dry and wet deposition of both particulate and gaseous emissions. Based on the guidance provided for application of the AERMOD model in Appendix W, and based on the history of deposition algorithms in the AERMOD and ISC models, the partic le deposition algorithms with a user-specified particle size distribution (referred to below as “Method 1”) can be applied unde r the regulatory default option. This option is comparable to the particle deposition algorithm in th e ISCST3 model (EPA, 1995a). The gas deposition algorithms and the “M ethod 2” option for particle deposition based on the ANL draft report (Wesely, et al, 2002) are considered to be non-DFAULT options in AERMOD, and the model will issue a fatal erro r message and abort processing if the DFAULT option is specified with the gas deposition or Method 2 particle de position options. As discussed above in Section 1.2, the TOXICS option formerly associated with the options for gas deposition and Method 2 for particle deposition is no longer used in the AERMOD model. No additional option switches are required to allow use of these non-DFAULT op tions. Table 1-1 in Section 1.2 summarizes the required keywords and regulatory status of various deposition options within
AERMOD. The remainder of this section provides a detailed de scription of the model input parameters associated with the deposition algorithms.

2.2.1 Definition of Seasons for Gas Dry Deposition

The gas deposition algorithms in AERMOD in clude land use characteristics and some gas deposition resistance terms based on five seas onal categories, defined in Table 2 of the ANL report as:30 Seasonal Category 1: Midsummer with lush vegetation Seasonal Category 2: Autumn with unharvested cropland Seasonal Category 3: Late autumn after fros t and harvest, or winter with no snow Seasonal Category 4: Winter with snow on ground (with generally continuous snow cover) Seasonal Category 5: Transitiona l spring with partial green coverage or short annuals

The user correlates these seasonal definiti ons to calendar months through the GDSEASON keyword on the CO pathway. The syntax a nd type of the GDSEASON keyword are:

Syntax: CO GDSEASON Jan Feb Mar ... Dec Type: Optional, Non-repeatable

where a numeric value from 1 to 5 is entered for each of the twelve calendar months to associate it with the seasonal definitions given above. This keyword is optional for the model, but mandatory when applying the gas deposition al gorithms, unless the GASDEPVD option for userspecified dry deposition velocity on the CO path way is used, described below in Section 2.2.5. Note that some of the seasonal categories defi ned above may not apply fo r certain regions, such as Category 4, winter with continuous snow cover, for moderate climates.

2.2.2 Definition of Land Use Cate gories for Gas Dry Deposition

The gas deposition algorithms include some ga s deposition resistance terms based on five seasonal categories, defined above, and nine land use categories as follows (from Table 1 of the ANL report):

Land Use Category Description 1 Urban land, no vegetation 2 Agricultural land 3 Rangeland 4 Forest 5 Suburban areas, grassy 6 Suburban areas, forested 7 Bodies of water 8 Barren land, mostly desert 9 Non-forested wetlands31 The user defines the land use categories by direction sector thr ough the GDLANUSE keyword on the CO pathway. The syntax and type of the GDLANUSE keyword are:

Syntax: CO GDLANUSE Sec1 Sec2 Sec3 ... Sec36 Type: Optional, Non-repeatable

where a numeric value from 1 to 9 is entered for each of the 36 direction sectors (every 10 degrees) to associate it with th e land use definitions given above. This keyword is optional for the model, but mandatory when applying the gas deposition algorithms, unless the GASDEPVD option for user-specified deposition velocity is us ed. The first value, Sec1, corresponds with the land use category, downwind of the application s ite, for winds blowing toward 10 degrees, plus or minus 5 degrees. The downwind sectors ar e defined in clockwise order, with Sec36 corresponding to winds blowing toward 360 degr ees (North), and should generally reflect
conditions downwind relative to the source locati on. The user can specify "repeat values" by entering a field such as "36*3" as a parame ter for the GDLANUSE keyword. The model will interpret this as "36 separate entries, each with a value of 3." Since the model must identify this as a single parameter field, there must not be any spaces between the repe at-value and the value to be repeated.

2.2.3 Option for Overriding Default Parameters for Gas Dry Deposition

An optional keyword is available on the Cont rol (CO) pathway to allow the user to
override the default values of the reactivity factor ( f

o ), and the fraction (F) of maximum green leaf area index (LAI) for seasona l categories 2 (autumn/unharvested cropland) and 5 (transitional spring), for use with the ga s dry deposition algorithms.

The syntax and type of the GASDEPD F keyword are summarized below:32 Syntax: CO GASDEPDF React F_Seas2 F_Seas5 (Refpoll) Type: Optional, Non-repeatable

where the parameter React is the valu e for pollutant reactivity factor ( f

o ), and F_Seas2 and F_Seas5 are the fractions (F) of maximum green LAI for seasonal categories 2 and 5, respectively. The parameter Refpoll is the optional name of the pollutant. If the optional GASDEPDF keyword is omitted, then the default value of 0 is used for React, and default values of 0.5 and 0.25 are used for F_Seas2 and F_Seas5, respectively. A value of F=1.0 is used for seasonal categories 1, 3, and 4. A reactivity fa ctor value of 1 should be input for ozone (O 3 ), titanium tetrachloride (TiCl 4 ), and divalent mercury (Hg 2+ ), and a value of 0.1 should be input for nitrogen dioxide (NO 2 ).

2.2.4 Specifying Source Parameters fo r Gas Deposition (Dry and/or Wet)

The input of source parameters for dry a nd wet deposition of gaseous pollutants is controlled by the GASDEPOS keyword on the SO pathway. The gas deposition variables may be input for a single source, or may be applied to a range of sources.

The syntax, type, and order for the GAS DEPOS keyword are summarized below:

Syntax: SO GASDEPOS Srcid (or Srcrng) Da Dw rcl Henry Type: Optional, Repeatable Order: Must follow the LOCATION card for each source input

where the Srcid or Srcrng identify the sour ce or sources for which the inputs apply, the parameter Da is the diffusivity in ai r for the pollutant being modeled (cm 2 /s), Dw is the diffusivity in water for the pollutant being modeled (cm 2 /s), rcl is the cuticular resistance to uptake by lipids for individual leaves (s/cm), and Henry is the Henry's Law constant (Pa

m 3 /mol). Values of the physical parameters fo r several common pollutants may be found in the appendices to the ANL report (Wesely, et. al, 2002).33 2.2.5 Option for Specifying the Deposition Velocity for Gas Dry Deposition

An optional keyword is available on the C ontrol (CO) pathway to allow the user to specify the dry deposition velocity for gaseous emissions. A single dry deposition velocity can be input for a given model run, and is used for all sources of gaseous pollutants. Selection of this option will by-pass the algorithm for computing de position velocities for ga seous pollutants, and should only be used when sufficien t data to run the algorithm are not available. Results of the AERMOD model based on a user-specified depo sition velocity should be used with extra
caution.

The syntax and type of the GASDE PVD keyword are summarized below:

Syntax: CO GASDEPVD Uservd Type: Optional, Non-repeatable

where the parameter Uservd is the gaseous dry deposition velocity (m/s). A non-fatal warning message is generated by the model if a value of Uservd greater than 0.05 m/s (5 cm/s) is input by the user. When the GASDEPVD keyword is used, the GDSEASON, GDLANUSE, and GASDEPRF keywords for the CO pathway, and the GASDEPOS keyword for the SO pathway, are no longer applicable and ca nnot be used in the same model run. As a result, gas wet deposition processes (DEPOS, WDEP, and WE TDPLT) cannot be simulated with the GASDEPVD option is used.

2.2.6 Specifying Source Parameters for Particle Deposition

The AERMOD model includes two methods for handling dry and/or wet deposition of particulate emissions. Method 1 is used when a significant fraction (greater than about 10 percent) of the total particul ate mass has a diameter of 10 μ m or larger, or when the particle size distribution is known. The partic le size distribution must be know n reasonably well in order to use Method 1. Method 2 may be used when the pa rticle size distribution is not well known and when a small fraction (less than 10 percent of th e mass) is in particles with a diameter of 10 μ m or larger. The deposition velocity for Method 2 is calculated as the weighted average of the34 deposition velocity for particles in the fine mode (i.e., less than 2.5 μ m in diameter) and the deposition velocity for the coarse mode (i.e., greater than 2.5 μ m but less than 10 μ m in diameter). As described in Sections 1.2 and 2.2, use of the Method 2 option is considered nonDFAULT.

2.2.6.1 Specifying Particle Inputs for Method 1

The input of source variables for particle de position using Method 1 is controlled by three keywords on the SO pathway, PARTDIAM, MASSFRAX, and PARTDENS. These inputs are comparable to the particulate inputs used in the ISCST3 mo del (EPA,1995a). The particle variables may be input for a si ngle source, or may be appl ied to a range of sources.

The syntax, type and order for these three keywords are summarized below:

Syntax: SO PARTDIAM Srcid (or Srcrng) Pdiam(i), i=1,Npd SO MASSFRAX Srcid (or Srcrng) Phi(i), i=1,Npd SO PARTDENS Srcid (or Srcrng) Pdens(i), i=1,Npd Type: Optional, Repeatable Order: Must follow the LOCATION card for each source input

where the Srcid or Srcrng identify the source or sources for which the inputs apply, and where the Pdiam array consists of the mass-mean aerodynamic particle diameter (microns) for each of the particle size categories, th e Phi array is the corresponding ma ss fractions (between 0 and 1) for each of the categories, and the Pdens arra y is the corresponding particle density (g/cm 3 ) for each of the categories.

The number of particle size cat egories for a particular sour ce is Npd. The user does not explicitly tell the model the number of categories being input, but if con tinuation cards are used to specify particle size variable s, all inputs of a keyword for a particular source or source range must be contiguous, and the number of categorie s must agree for each of the three keywords input for a particular source. As many continua tion cards as needed may be used to define the inputs for a particular keyword. The model checks the inputs to ensure that the mass fractions35 sum to 1.0 (within 2 percent) for each source input, and issues a warning message if that range is
exceeded. The model also ensures that mass fracti ons for each particle size category are within the proper range (between 0 and 1), and issues fatal error messages for any value exceeded that

range.

2.2.6.2 Specifying Particle Inputs for Method 2

The Method 2 particle info rmation is input through the METHOD_2 keyword on the SO pathway. The syntax, type, and order for th e METHOD_2 keyword are summarized below:

Syntax: SO METHOD_2 Srcid (or Srcrng) FineMassFraction Dmm Type: Optional, Repeatable Order: Must follow the LOCATION card for each source input

where the Srcid or Srcrng identify the sour ce or sources for which the inputs apply, the parameter FineMassFraction is the fraction (between 0 and 1) of particle mass emitted in the fine mode, less than 2.5 microns, and Dmm is the representative mass-mean aerodynamic particle
diameter in microns. Estimated values of fine particle fractions and mass mean diameters for various pollutants are provided in Appendix B of the ANL report (Wesely, et al, 2002).

2.2.7 Specifying Emission and Output Units

Since the AERMOD model allows for both con centration and depositio n to be output in the same model run, the EMISUNIT keyword (see Section 3.3.6 of the AERMOD User’s Guide (EPA, 2004a)) cannot be used to specify emission un it factors if more than one output type is being generated. The AERMOD model therefore allows for concentration and deposition units to be specified separately through the CONC UNIT and DEPOUNIT keywords, respectively. The syntax and type of the CONCUN IT keyword are summarized below:36 Syntax: SO CONCUNIT Emifac Emilbl Conlbl Type: Optional, Non-repeatable

where the parameter Emifac is the factor to c onvert emission rate input units to the desired output units, Emilbl is the label fo r the emission input units (up to 40 characters), and Conlbl is the output unit label (up to 40 char acters) for concentration calcula tions. The syntax and type of the DEPOUNIT keyword are summarized below:

Syntax: SO DEPOUNIT Emifac Emilbl Deplbl Type: Optional, Non-repeatable

where the parameter Emifac is the factor to c onvert emission rate input units to the desired output units, Emilbl is the label fo r the emission input units (up to 40 characters), and Deplbl is the output unit label (up to 40 charac ters) for deposition calculations.

2.2.8 Deposition Velocity and Resistance Outputs

In order to facilitate revi ew and testing of the depositi on algorithms in the AERMOD model, the model includes an opt ion to output the main resistan ce terms and deposition velocities for gaseous and particle sources. These optional outputs are genera ted if the user specifies the ‘CO DEBUGOPT MODEL’ option described in Section 3.2.13 of the AERMOD User’s Guide (EPA, 2004a). The gas deposition data are writ ten to a file called GDEP.DAT, which includes
the values of R a , R b , R c , and V dg

(see Wesely, et al, 2002, for de finitions) for each source and for
each hour modeled. A header record is included to identify the columns. The particle deposition
data are written to a file called PD EP.DAT, which includes the values of R a , R p , V g , and V d for each source and for each hour modeled. The particle outputs are labeled as being based on either
Method 1 or Method 2. For Method 1, results are output for each particle size category. The
filename and file units for these data files are hardcoded in the m odel, and the files are
overwritten each time the model is executed. Si nce these files include data for each source for each hour, file sizes may become large.37 2.2.9 Meteorological Data for Deposition Algorithms

The AERMET meteorological processor was modi fied (beginning with the version dated 04300) to output additional meteorological parame ters needed for the deposition algorithms in
AERMOD. The additional variables include th e precipitation code, precipitation rate, relative humidity, surface pressure, and cloud cover. These additional variables are automatically
included after the standard variab les for each hour, and do not require any additional user input. The precipitation data needed for wet deposition calculations in AERMOD can be obtained from the SAMSON, HUSWO or ISHD (TD-3505) formats currently supported by AERMET (EPA, 2004b).

The input meteorological data file consists of a header record that includes the latitude and longitude, surface station ID (e.g., WBAN numb er), upper air station ID , the on-site station ID, and the AERMET version date (see Section D.1 of the AERMOD model user = s guide (EPA, 2004a)). The meteorological data file for the depositi on algorithms is read as a free format file, i.e., each field on a record is separated from adjacent fields by a comma or by one or more spaces. The subsequent data records contain the following variables in the order listed:

Variable Description Format Year Integer Month Integer Day of Month Integer Julian Day (Day of Year) Integer Hour of Day Integer Heat Flux (W/m 2 ) Real Surface Friction Velocity, u * (m/s) Real Convective Velocity Scale, w * (m/s) Real Lapse Rate above Mixing Height (K/m) Real Convective Mixing Height (m) Real Mechanical Mixing Height (m) Real Monin-Obukhov Length, L (m) Real Surface Roughness Length, z o (m) Real Bowen Ratio Real Albedo Real Reference Wind Speed (m/s) Real Reference Wind Direction (degrees) Real Reference Height for Wind (m) Real38 Ambient Temperature (K) Real Reference Height for Temperature (m) Real Precipitation Code (0-45) Integer Precipitation Amount (mm) Real Relative Humidity (%) Real Surface Pressure (mb) Real Cloud Cover (tenths) Integer

2.3 OPEN PIT SOURCE OPTION

The open pit source option is invoked by speci fying a source type of OPENPIT on the source location (SO LOCATION) card. The OPENPI T source algorithm can be used to model particulate or gaseous emissions from open pits, su ch as surface coal mines and rock quarries. If particulate emissions are modeled, the user must specify the part icle size information through the appropriate keywords described in Section 2.2. The OPENPIT algor ithm uses an effective area for modeling pit emissions, based on meteorologi cal conditions, and then utilizes the numerical integration area source algorithm to model the impact of emissions from the effective area sources. A complete technical description of the OPENPIT source algorith m is provided in the
ISC3 Model User = s Guide - Volume II (EPA, 1995b).

The AERMOD model accepts rectangular pits w ith an optional rotation angle specified
relative to a north-south orientati on. The rotation angle is specified relative to the vertex used to
define the source location on the SO LOCATION card (e.g., the southwest corner). The syntax, type and order for the SRCPARAM card for OP ENPIT sources are summarized below:

Syntax: SO SRCPARAM Srcid Opemis Relhgt Xinit Yinit Pitvol (Angle) Type: Optional, Repeatable Order: Must follow the LOCATION card for each source input

where the Srcid parameter is the same source ID that was entered on the LOCATION card for a particular source, and the othe r parameters are as follows:

Opemis - open pit emission rate in g/(s-m 2 ),39 Relhgt - average release height above the base of the pit in meters,
Xinit - length of X side of the open pit (in the east-west direction if Angle is 0 degrees) in meters,
Yinit - length of Y side of the open pit (in the north-south direction if Angle is 0 degrees) in meters,
Pitvol - volume of open pit in cubic meters, and
Angle - orientation angle for the rectangular open pit in de grees from North, measured positive in the clockwise direction (optional).

The same emission rate is used for both c oncentration and depositi on calculations in the
AERMOD model. It should also be noted that the emission rate for the open pit source is an emission rate per unit area, which is different fr om the point and volume source emission rates,
which are total emissions for the source. The Re lhgt parameter cannot exceed the effective depth of the pit, which is calculated by the model base d on the length, width and volume of the pit. A Relhgt of 0.0 indicates emissions that ar e released from the base of the pit.

If the optional Angle parameter is input, and the value does not equal 0.0, then the model will rotate the open pit clockwise around the vert ex defined on the SO LOCATION card for this source. The relationship between the Xinit, Yini t, and Angle parameters and the source location, (Xs,Ys), for a rotated pit is the same as for rectangular area sources. The Xinit dimension is
measured from the side of the area that is c ounterclockwise along the perimeter from the vertex defined by (Xs,Ys), while the Yinit dimension is m easured from the side of the open pit that is clockwise along the perimeter from (Xs,Ys). Un like the area source inputs , the Yinit parameter is not optional for open pit sources. The Angle pa rameter is measured as the orientation relative
to North of the side that is cloc kwise from (Xs,Ys), i.e. the side with length Yinit. The Angle parameter may be positive (for clockwise rotatio n) or negative (for counterclockwise rotation), and a warning message is generated if the absolute value of Angle is grea ter than 180 degrees.
The selection of the vertex to use for the source location is not critical, as long as the relationship described above for the Xinit, Yinit, and Angle parameters is maintained.40 The aspect ratio (i.e., length/width) of open pit sources should be less than 10 to 1. However, since the pit algorithm generates an ef fective area for modeling emissions from the pit, and the size, shape and location of the effective area is a function of wind direction, an open pit
cannot be subdivided into a series of smaller sour ces. Aspect ratios of greater than 10 to 1 will be flagged by a warning message in the output fi le, and processing will continue. Since open pit sources cannot be subdivided, the user should characterize irregularly -shaped pit areas by a rectangular shape of equal area. Receptors shou ld not be located within the boundaries of the pit; concentration and/or deposition at such recepto rs will be set to zero. Such receptors will be identified during model setup and will be flagged in the summary of inputs.

An example of a valid SRCPARAM input card for an open pit source is given below:

SO SRCPARAM NORTHPIT 1.15E-4 0.0 150.0 500.0 3.75E+6 30.0

where the source ID is NORTHPIT, the emission rate is 1.15E-4 g/(s-m 2 ), the release height is 0.0 m, the X-dimension is 150.0 m, the Y-dimensi on is 500.0 m, the pit volume is 3.75E+6 cubic meters (corresponding to an effective pit depth of about 50 meters) and the orientation angle is 30.0 degrees clockwise from North.41 2.4 LINE SOURCE OPTION

Beginning with version 12345, a LINE source type has been added to the SO pathway. The LINE source option is invoked by specifying a source type of LINE on the source location (SO LOCATION) card. The LINE source type opti on allows users to speci fy line-type sources based on a start-point and end-point of the line and the width of the line, as an alternative to the current AREA source type for rectangular sour ces. The LINE source type utilizes the same routines as the AREA source type , and will give identical results for equivalent source inputs. The LINE source type also includes an optional initial sigma-z parameter to account for initial
dilution of the emissions. As with the AREA so urce type, the LINE source type does not include the horizontal meander component in AERMOD. Si nce the LINE source type utilizes the AREA source algorithms, the runtime optimizations asso ciated with the FAST AREA option will also apply to LINE sources if included.

The syntax, type and order for the LOCATI ON card for LINE sources are summarized
below:

Syntax: SO LOCATION Srcid LINE Xs1 Ys1 Xs2 Ys2 (Zs) Type: Mandatory, Repeatable Order: Must be the first card for each source input

where the Srcid parameter is the user-speci fied source ID, Xs1 and Ys1 are the x and y coordinates for the midpoint of one end of the LINE, Xs2 and Ys2 are the x and y coordinates for the midpoint of the other end of the LINE, and Zs is the optional elevati on of the source above
sea-level.

The syntax, type and order for the SRCPAR AM card for LINE sources are summarized
below:42 Syntax: SO SRCPARAM Srcid Lnemis Relhgt Width (Szinit) Type: Mandatory, Repeatable Order: Must follow the LOCATION card for each source input

where the Srcid parameter is the same source ID that was entered on the LOCATION card for a particular source, and the othe r parameters are as follows:

Lnemis - line source emission rate in g/(s-m 2 ),
Relhgt - average release height above gr ound in meters (unless ELEVUNIT keyword is used to specify elev ations in feet),

Width - width of the source in mete rs (with a minimum width of 1m),

Szinit - initial vertical dimension of the line source in meters (optional),

As noted above, the LINE source type option in AERMOD uses the same algorithms as used for the AREA source type for rectangular sources, and will give identical results for equivalent
source definitions. The LINE s ource emission rate is in g/(s-m 2 ) and the model assumes that emissions are uniformly distributed across the di mensions of the LINE source. As with the AREA source type, the LINE source type does not include the horizontal meander component that is incorporated for POIN T and VOLUME sources. Also, as with the AREA source type, the LINE source type will estimate c oncentrations (and/or de position) at receptor s located within the
dimensions of the source.

2.5 SPECIFYING BACKGR OUND CONCENTRATIONS

Beginning with version 11059, users can spec ify uniform or temporally varying background concentrations using the BACKGR ND keyword on the SO pathway. Background
concentrations can be included with any source group to estimate cumulative ambient impacts. Background concentrations can be specified using a range of options similar to those available with the EMISFACT keyword for source emissions, or on an hourly basis from a separate data file. The syntax of the BAC KGRND keyword is as follows:43 Syntax: SO BACKGRND BGflag BGvalue(i), i=1,n and/or SO BACKGRND HOURLY BGfilnam (BGformat) Type: Optional, Repeatable

where the BGflag parameter is the variable background concentra tion flag, BGvalue is the array of background concentration values associated with BGflag, HOURLY indicates use of an hourly background file, BGfilnam is the filename for the hourly background data, and BGformat is the optional Fortran format of the hourly back ground file (‘free’ format is used by default).
The BGfilnam can be up to 200 characters in length based on the default parameters in AERMOD. Double quotes (“) at the beginning and end of the filename can also be used as field delimiters to allow filenames with embedded spaces.

The HOURLY background file must include the year, month, day, and hour, followed by the background concentration, in that orde r (unless specified differently through the BGformat parameter). The year can be specified as either a 2-digit or 4-digit year . If an optional Fortran format is specified using the BGformat paramete r, the year, month, day, and hour variables must be read as integers using the Fortran I format, and the background concentration must be read as a real variable, using the Fortra n F, E, or D format, e.g., (4I2,F8.3). The BGformat parameter must include the open and close parentheses as shown in the example, and may also include embedded spaces if double quotes (“) are used to delimit the field. A warning message will be generated if the specified format does not m eet these requirements, and AERMOD may also issue a fatal error message when reading the file in cases where real variables are read with an integer format, or vice versa.

If the optional BGformat parameter is missing, then the model will read the background data using a Fortran free format, i.e., assuming that commas or spa ces separate the data fields, in the order given above. The date sequence in the background data file must also match the date sequence in the hourly meteor ological data files.44 Note that the HOURLY option and an option to specify values based on the BGflag parameter can both be specified in the same mo del run. This allows the user to specify background concentrations on a temporal ly-varying basis, such as SEASHR , that can be used to substitute for missing values in an hourly b ackground file. Otherwise, AERMOD will issue a fatal error message and abort processing if missing data are encountered in an HOURLY background file. Background con centration units can be spec ified using the BACKUNIT keyword, described below. If the BACKUNIT keyword is omitted, default units of PPB are assumed for background NO 2 and SO 2 , PPM for CO, and UG/M3 for all other pollutants. Background concentrations specified in units of PPB or PPM are converted to UG/M3 based on reference temperature (25 C) and pressure (1013.25 mb).

To include background concentrations with a particular source group, the reserved
“source ID” of BACKGROUND can be included on the SRCGROUP keyword, including source group ALL. The contribution of background con centrations can be tracked separately by including a source group with BACKGR OUND as the only “source ID.” NOTE: The source of background concentrations and the me thod used to incorporate background concentrations in a cumulative impact assessment involves several considerations and should be documented and justified on a case-by-case basis.

Background concentrations specified with the BACKGRND keyword are combined with source impacts on a temporally-paired basis to es timate cumulative ambient impacts. However,
since modeled concentrations are not calculate d for hours with calm or missing meteorological data, background concentrations are also omitted for those hours. This may result in the background contribution being lower than expected for short-term averages of 3-hours up to 24- hours for periods when the denominator used to calculate the multi-hour average is adjusted in accordance with EPA’s calms policy (see Sectio n 8.3.4.2 of Appendix W), which is implemented within the AERMOD model. For example, if 12 hours out of a 24-hour period are calm or missing, the calms policy dictates that the 24-hour average concentration would be based on the sum of the 12 non-calm/non-missing hours divide d by 18. The contribution from background
concentrations would also be based on the sum of background values for the 12 non-calm/nonmissing hours, divided by 18. If background wa s specified as uniform during that 24-hour45 period, then the contribution from background woul d appear to be 33.3% lower than expected (i.e., 12/18).

The BGflag parameter must be specified as one of the following secondary keywords (the number in parentheses indicates the numb er of values required for each option):

ANNUAL - annual background value (n=1),

SEASON - background values vary seasonally (n=4),

MONTH - background values vary monthly (n=12),

HROFDY - background values vary by hour-of-day (n=24),

WSPEED - background values vary by wind speed (n=6),

SEASHR - background values vary by season and hour-of-day (n=96),

HRDOW - background values vary by hour-of-da y, and day-of-week [M-F, Sat, Sun] (n=72),

HRDOW7 - background values vary by hour-of-da y, and the seven days of the week [M, Tu, W, Th, F, Sat, Sun] (n=168),

SHRDOW - background values vary by season, hour-of-day, and day-of-week [M-F, Sat, Sun] (n=288),

SHRDOW7 - background values vary by season, hou r-of-day, and the seven days of the week [M, Tu, W, Th, F, Sat, Sun] (n=672),

MHRDOW - background values vary by month, hour-of-day, and day-of-week [M-F, Sat, Sun] (n=864), and

MHRDOW7 - background values vary by month, hou r-of-day, and the seven days of the week [M, Tu, W, Th, F, Sat, Sun] (n=2,016).

The seasons are defined in the following order: Winter (Dec., Jan., Feb.), Spring (Mar., Apr., May), Summer (Jun., Jul., Aug.), and Fall (Sep., Oct., Nov.). The wind speed categories used with the WSPEED option may be defined using the ME WINDCATS keyword. If the WINDCATS keyword is not used, the default wind speed categories are defined by the upper bound of the first five categories as follows (the sixth category is assumed to have no upper46 bound): 1.54, 3.09, 5.14, 8.23, and 10.8 m/s. The BACKGR ND keyword may be repeated as many times as necessary to input all of the back ground values, and repeat values may be used for the numerical inputs.

Background concentration units can be speci fied on the optional BACKUNIT keyword on the SO pathway. The syntax of th e BACKUNIT keyword is as follows:

Syntax: SO BACKUNIT BGUnits Type: Optional, Non-repeatable

where the BGUnits parameter specifies the units as parts-per-billion (PPB), parts-per-million (PPM), or micrograms/cubic-meter (UG/M3). Units specified on the BACKUNIT keyword are applied to HOURLY and temporally-varying backgr ound values if both are included in the same model run. If the BACKUNIT keyword is om itted, default units of PPB are assumed for background NO 2 and SO 2 , PPM for CO, and UG/M3 for all other pollutants. Background concentrations specified in units of PPB or PPM are converted to UG/M3 based on reference temperature (25 C) and pressure (1013.25 mb).

2.6 PVMRM AND OLM OPTIONS FOR MODELING NO 2

This section provides a description of th e inputs related to the non-DFAULT PVMRM and OLM options for modeling the conversion of NO x to NO 2 . A technical description of the PVMRM algorithm is provided in an Adde ndum to the AERMOD Model Formulation Document (Cimorelli, et al. , 2004). Background on the original development of the PVMRM option is provided by Hanrahan (1999a and 1999b).

The PVMRM and OLM algorithms have been implemented as non-DFAULT options, which means that the PVMRM and OLM options cannot be used if the DFAULT keyword is
included on the CO MODELOPT card. As descri bed in Section 2.1.1, a BETA-test draft model option, PSDCREDIT, has been added for use when an application is for increment consumption47 with PSD credits using PVMRM. The special source grouping required for the PSDCREDIT option is described below in Section 2.6.6.1.

2.6.1 Specifying Ozone Concentrations for PVMRM and OLM Options

The background ozone concentrations for th e PVMRM and OLM options can be input as a single value through the OZONE VAL keyword on the CO pathway, as temporally-varying values through the O3VALUES keyword on the CO pathway, or as hourly values from a separate data file specified through the OZONEFIL keyword on the CO pathway. The user must specify background ozone concentrations through the OZONEVAL, O3VALUES, or OZONEFIL keyword in order to use the PVMRM or OLM options. The OZONEVAL or O3VALUES keyword may also be specified wi th the OZONEFIL keyword, in which case the value(s) entered on the OZONEVAL or O3VALUES keyword will be used to substitute for hours with missing ozone data in the hourly ozone data file.

The syntax of the OZONEVAL keyword is as follows:

Syntax: CO OZONEVAL O3Value (O3Units) Type: Optional, Non-repeatable

where the O3Value parameter is the background ozone concentration in the units specified by the optional O3Units parameter (PPM, PPB, or UG/M3 ). If the optional O3Units parameter is missing, then the model will assume units of micrograms/cubic-meter (UG/M3) for the background ozone values. If units of PPM or PPB are used, then the model will convert the concentrations to micrograms/cubic-meter based on reference temperature (25 C) and pressure (1013.25 mb).

The syntax of the O3VALUES keyword is as follows, and is similar to the EMISFACT keyword on the SO pathway for specifyi ng temporally-varying emission rates:48 Syntax: CO O3VALUES O3Flag O3values(i), i=1,n Type: Optional, Repeatable

where the parameter O3Flag is the variable ozone concentration flag, and must be specified as one of the following secondary keywords (the nu mber in parentheses i ndicates the number of values required for each option):

ANNUAL - annual ozone value (n=1); equiva lent to OZONEVAL keyword in PPB,

SEASON - ozone values vary seasonally (n=4),

MONTH - ozone values vary monthly (n=12),

HROFDY - ozone values vary by hour-of-day (n=24),

WSPEED - ozone values vary by wind speed (n=6),

SEASHR - ozone values vary by season and hour-of-day (n=96),

HRDOW - ozone values vary by hour-of-day, and day-of-week [M-F, Sat, Sun] (n=72),

HRDOW7 - ozone values vary by hour-of-day, and the seven days of the week [M, Tu, W, Th, F, Sat, Sun] (n=168),

SHRDOW - ozone values vary by season, hour-of-day, and day-of-week [M-F, Sat, Sun] (n=288),

SHRDOW7 - ozone values vary by season, hour-of- day, and the seven days of the week [M, Tu, W, Th, F, Sat, Sun] (n=672),

MHRDOW - ozone values vary by month, hour-o f-day, and day-of-week [M-F, Sat, Sun] (n=864), and

MHRDOW7 - ozone values vary by month, hour-of- day, and the seven days of the week [M, Tu, W, Th, F, Sat, Sun] (n=2,016).

The O3Values array is the array of ozone va lues, where the number of values is shown above for each O3Flag option. The seasons are defined in the following order: Winter (Dec., Jan., Feb.), Spring (Mar., Apr., May), Summer (Jun., Jul., Aug.), and Fall (Sep., Oct., Nov.). The wind speed categories used with the WSPE ED option may be defined using the ME49 WINDCATS keyword. If the WINDCATS keywor d is not used, the default wind speed categories are defined by the uppe r bound of the first five cate gories as follows (the sixth category is assumed to have no upper bound): 1.54, 3.09, 5.14, 8.23, and 10.8 m/s. The O3VALUES keyword may be repeated as many times as necessary to input all of the ozone values, and repeat values may be used for the numerical inputs.

The order of inputs specified for the hour-of-day/day-of-week options (HRDOW, SHRDOW, SHRDOW7, etc.) are by hour-of-day, then season or month, if applicable, and then by day-of-week. For the HRDOW/SHRDOW/MHRDOW options, the days of the week are specified in the order of Weekdays (M -F), Saturdays, and Sundays. For the
HRDOW7/SHRDOW7/ MHRDOW 7 options, the days of the week are specified in the order of Mondays, Tuesdays, etc., through Sundays. Sec tion 2.6.1 below includes an example illustrating the order of inputs for these opt ions for the EMISFACT keyword.

Ozone concentrations specifi ed on the O3VALUES keyword are assumed to be in units of PPB unless the OZONUNIT keyword is specifie d. The syntax of the OZONUNIT keyword is
as follows:

Syntax: CO OZONUNIT OzoneUnits Type: Optional, Non-repeatable

where the OzoneUnits parameter specifies the units as parts-per-billion (PPB), parts-per-million (PPM), or micrograms/cubic-meter (UG/M3). Units specified on the CONCUNIT keyword are only applied to ozone concentrations input thought O3VALUES keyword, which assumes default units of PPB if the OZONUNIT keywor d is not specified. Ozone concentrations specified in units of PPB or PPM are converted to UG/M3 based on reference temperature (25 C) and pressure (1013.25 mb).

The syntax of the OZONEFIL keyword is as follows:50 Syntax: CO OZONEFIL O3FileName (O3Units) (O3Format) Type: Optional, Non-repeatable

where the O3FileName parameter is the filename for the hourly ozone concentration file, the optional O3Units parameter specifies the units of the ozone data (PPM, PPB, or UG/M3, with UG/M3 as the default), and the optional O3Format parameter specifies the Fortran format to read the ozone data. The O3FileName can be up to 200 characters in leng th based on the default parameters in AERMOD. Double quotes (“) at the beginning and end of the filename can also be
used as field delimiters to allow filenames with embedded spaces.

The hourly ozone file must include the y ear, month, day, and hour, followed by the ozone concentration, in that order (unle ss specified differently through the O3Format parameter). The year can be specified as either 2- digit or 4-digit year. If an op tional Fortran format is specified using the O3Format parameter, the year, month, day, and hour variables must be read as integers using the Fortran I format, and the ozone concentrat ion must be read as a real variable, using the Fortran F, E, or D format, e.g., (4I2,F8.3). The O3Format parameter must include the open and close parentheses as shown in the example, and may also include embedded spaces if double quotes (“) are used to delimit the field. A warn ing message will be generated if the specified format does not meet these requirements, and AERMOD may also issue a fatal error message when reading the file in cases wher e real variables are r ead with an integer format, or vice versa.

If the optional O3Format parameter is missing, then the model will read the ozone data using a Fortran free format, i.e., assuming that co mmas or spaces separate the data fields, in the order given above. The date sequ ence in the ozone data file must match the date sequence in the hourly meteorological data files. As with th e OZONEVAL keyword, if units of PPM or PPB are used, then the model will convert the concen trations to micrograms/cubic-meter based on reference temperature (25 C) and pressure (1013.25 mb).

Values of ozone concentrations in the ozone da ta file that are less than zero or greater than or equal to 900.0 will be regarded as mi ssing. If background ozone values have been specified using the OZONEVAL or O3VALUES keyword, then the appropriate value will be51 used to substitute for missing ozone data from the ozone file. If no OZONEVAL or O3VALUES keywords are used, then the mode l will assume full conversion for hours with missing ozone data.

2.6.2 Specifying the Ambient Equilibrium NO 2 /NO x Ratio for PVMRM and OLM

The PVMRM option for modeling conversion of NO to NO 2 incorporates a default
NO 2 /NO x ambient equilibrium ratio of 0.90. Be ginning with version 11059 of AERMOD, a default equilibrium ratio of 0.90 has also b een incorporated in the OLM option. A NO 2 /NO x equilibrium ratio other than 0.90 can be specifi ed for either the PVMRM or OLM option through the optional NO2EQUIL keyword on the CO path way. The syntax of the NO2EQUIL keyword
is as follows:

Syntax: CO NO2EQUIL NO2Equil Type: Optional, Non-repeatable

where the NO2Equil parameter is the NO 2 /NO x equilibrium ratio and must be between 0.10 and 1.0, inclusive.

2.6.3 Specifying the Default In-stack NO 2 /NO x Ratio for PVMRM and OLM

The PVMRM and OLM options for modeling conversion of NO to NO 2 require that an
in-stack NO 2 /NO x ratio be specified. Based on guidan ce issued June 28, 2010, regarding the 1-
hour NO 2 NAAQS, AERMOD has been modified to require the user to specify in-stack
NO 2 /NO x ratios for each source under the OLM a nd PVMRM options, i.e., AERMOD no longer
assumes a default in-stack ra tio of 0.10 for the OLM option.

The in-stack NO 2 /NO x ratio can be specified for the PVMRM or OLM options by using either the CO NO2STACK card to specify a default value to be used for all sources, or by using the SO NO2RATIO card to specify a value on a s ource-by-source basis. The SO NO2RATIO52 card can also be used to ove rride the default value if th e CO NO2STACK card has been specified. The syntax of the NO2 STACK keyword is as follows:

Syntax: CO NO2STACK NO2Ratio Type: Optional, Non-repeatable

where the NO2Ratio parameter is the default in-stack NO 2 /NO x ratio that will be used, unless overridden on a source-by-source basis by the SO NO2RATIO card (described below). The value of NO2Ratio must be between 0.0 and 1.0, in clusive. Users should note that while CO NO2STACK is an optional keyword, the OLM and PVMRM options require the user to specify
an in-stack NO 2 /NO x ratio for each source, using either the CO NO2STACK or SO NO2RATIO cards (described in Section 2.6.4), or both.

2.6.4 Specifying In-stack NO 2 /NO x Ratios by Source for PVMRM and OLM

As noted above, the PVMRM and OLM options for modeling NO 2 conversion require instack NO 2 /NO x ratios to be specified for each source, i.e., AERMOD no longer assumes a default in-stack ratio of 0.10 for the OLM opti on. The user can specify in-stack NO 2 /NO x ratios through the optional NO2RATIO keyword on the SO path way. The syntax of the NO2RATIO keyword
is as follows:

Syntax: SO NO2RATIO SrcID or SrcRange NO2Ratio Type: Optional, Repeatable Order: Must follow the LOCATION card for each source input

where the SrcID or SrcRange identify the sour ce or sources for which the inputs apply, and where the NO2Ratio parameter specifies the in-stack ratio. In this way, the user can specify a single in-stack NO 2 /NO x ratio for a group of stacks. For example, the following input:

SO NO2RATIO STACK1-STACK10 0.1553 will apply the in-stack ratio of 0.15 to sources with IDs falling within the range STACK1 to STACK10. Any value specified on the SO NO2RA TIO card will override the default ratio, if any, specified on the CO NO2STACK card. Users s hould note that while SO NO2RATIO is an optional keyword, the PVMRM option requires the user to specify an in-stack NO 2 /NO x ratio for each source, using either the CO NO2STACK (d escribed in Section 2.6.3) or SO NO2RATIO cards, or both.

2.6.5 Specifying Combined Plumes for OLM

The OLM option for modeling NO 2 conversion includes an op tion for specifying which sources are to be modeled as combined plumes, i.e., where the NOx within the plumes competes for the available ambient ozone. Sources which are not specified for modeling as combined plumes will be modeled as individual plumes, i.e., where all of the ambient ozone is available for
conversion of NO to NO 2 . The selection of individual or combined plume option for OLM is specified through the OLMGROUP keyword on the SO pathway. The syntax of the
OLMGROUP card is as follows:

Syntax: SO OLMGROUP OLMGrpID SrcID’s and/or SrcRange’s

or SO OLMGROUP ALL Type: Optional, Repeatable (except for OLMGROUP ALL) Order: Must follow the LOCATION card for each source input; OLMGROUP ALL must follow the LOCATION card for all sources

where OLMGrpID identifies a group to be treat ed as a combined plume with OLM, and the SrcID's and/or SrcRange's identify the sources to be included in the OLM group. As with the SO SRCGROUP card, individual source IDs and source ra nges may be used on the same card, and if more than one input card is needed to defi ne the sources for a particular OLM group, then additional cards may be input by repeating th e pathway, keyword and OLM group ID. A user can also specify an OLMGrpID of ALL, which means that OLM will be applied on a combined plume basis to all sources. However, unlike th e SO SRCGROUP card, the results will not be54 output for an OLM group unless the same group of sources is also identified on a SRCGROUP
card. Another constraint is that a source canno t be included in more than one OLM group.
/
If a source is not selected for an OLMGRO UP card, then OLM will be applied to that source as an individual plume. Other than the similarity in synt ax, there is no connection in the model between the groups defined on the OLMGROUP card and groups defined on the
SRCGROUP card. The OLMGROUP card relates to how the result s are processed within the model for the OLM model, and the SRCGROUP card simply controls how source impacts are grouped in the model outputs.

If the user identifies one or more groups of sources to apply OLM on a combined plume basis using the OLMGROUP card, the model will st ill need to calculate the concentration for individual plumes within the OL M group in order for the model to sum the results for the sources listed on the SRCGROUP card(s). The individua l source concentrations are calculated by applying the ratio of the combined concentra tion for the OLM group with and without OLM to each source within the OLM group.

2.6.6 Modeling NO 2 Increment Credits with PVMRM

Due to the ozone-limiting effects of the PVMR M option, the predicted concentrations of
NO 2 are not linearly proportional to the emission rate. Therefore, the approach of modeling NO 2 increment consumption with PSD cr edits through the use of a nega tive emission rate for credit sources cannot be used with the PVMRM op tion. However, the draft PSDCREDIT option allows modeling PSD increment credits for NO 2 when the PVMRM option is specified. The PSDCREDIT option is currently implemented as a BETA-test option, and requires that the PVMRM and BETA options be specified. Th e PSDCREDIT option utilizes a new PSDGROUP keyword, described below, to identify which sour ces consume or expand increment. This option is not valid if the OLM option is specified, and no comparable option is available for modeling increment credits with the OLM option. The user should check with the appropriate reviewing authority for further guidance on modeling increment credits for NO 2 .55 A general discussion of concepts related to modeling increment consumption is provided below, followed by a description of inputs requ ired to use the BETA -test PSDCREDIT option
for PVMRM.

2.6.6.1 Increment Consuming and Baseline Sources

Increment is the maximum allowable increase in concentration of a pollutant above a
baseline concentration for an area defined unde r the Prevention of Significant Deterioration (PSD) regulations. The PSD baseline area can be an en tire State or a subregion of a State such as a county or group of counties. Increment standards exist for three pollutants: SO 2 (3-hr, 24-hr, and annual averages), NO 2 (annual average), and PM-10 (24-hr and annual average). Increment consumption is the additiona l air quality impact above a baseline concentration.

The baseline concentration is the ambient con centration of the polluta nt that existed in
the area at the time of the submittal of the first co mplete permit application by any source in that area subject to PSD regulations. A baseline source is any source that existed prior to that first application and the baseline date is the date of the PSD application. This baseline date is referred
to as the minor source baseline date in PSD regulations. By definition, baseline sources do not consume increment. However, any baseline sour ce that retires from service after the baseline date expands the increment available to new sources. Therefore, a PSD modeling analysis performed for a new source may need to account for this increment expansion. Such an analysis may therefore involve identification of three gro ups of sources: 1) increment-consuming sources; 2) retired (increment-expanding) baseline sources ; and 3) existing, non-retired, baseline sources.

2.6.6.2 Calculating Increment Consumption under the PSDCREDIT Option

Calculating increment consumption under th e PSDCREDIT option in AERMOD is not a simple arithmetic exercise invol ving the three groups of sour ces defined above. Since the
amount of ozone available in the atmos phere limits the conversion of NO to NO 2 , interactions of plumes from the existing and retired baseline so urces with those from the increment consuming sources must be considered as part of the calc ulation of net increment consumption. Without the56 PSDCREDIT option, properly accoun ting for the potential intera ction of plumes among the different source categories would require post-processing of results from multiple model runs. Internal “post”-processing al gorithms have been incorporated in AERMOD under the PSDCREDIT option to account for the apportioning of the three groups of sources to properly calculate increment consump tion from a single model run.

Define the following three source groupi ngs for the discussion that follows:

A = increment-consuming sources;
B = non-retired baseline sources; and
C = retired baseline, increment-expanding sources.

The calculation of the amount of increment consumption by the A sources cannot simply be estimated by modeling the A sources alone because of the possi ble interaction of those plumes with the plumes from B sources. The PVMRM algorithm is designed to account for such plume
interactions and calculate the total NO to NO 2 conversion in the combined plumes based on the amount of ozone available. Therefore, the total increment consumption by the A sources is given by the difference between (1) the total futu re impact of increment consuming sources and non-retired baseline sources ( A + B ) and (2) the total current impact ( B ), which can be expressed as ( A + B ) – ( B ). Here ( A + B ) represents the value that would be compared against the National Ambient Air Quality Standard (NAAQS) for NO 2 during PSD review of the A sources.

In a case where some of the baseline sour ces have been retired from service ( C sources), the PSD regulations allow the c onsideration of increment expans ion when assessing compliance with the PSD increment. However, the amount of increment expansion cannot be estimated by simply modeling the C sources alone because of the possible interaction of those plumes with the plumes from B sources. Therefore, the total increment expansion, i.e., PSD credit, is calculated as the difference between (1) the total impact prior to the retirement of C sources, i.e. ( B + C ), and (2) the total impact from existi ng (non-retired) baseline sources ( B ), which can be expressed as ( B + C ) – ( B ).57 Finally, the net increment consumption is gi ven by the difference between total increment consumption and the total increment expansion, or

[( A + B ) – ( B )] – [( B + C ) – ( B )] (1)

Note that in the absence of any increment expa nsion, the net increment consumption is equal to the total increment consumption [( A + B ) – ( B )], as described above.

These expressions of net increment consump tion and expansion cannot be interpreted as algebraic equations. Instead, the terms within parentheses represen t the results of separate model
runs that account for the combined effects of NO x conversion chemistry on specific groups of sources. The expression shown in Equation 1 above represents four model simulations: ( A + B ), ( B ), ( B + C ), and ( B ) again. In this case, the two ( B ) terms do cancel each other and we are left
with:

[( A + B )] – [( B + C )] (2)

The expression presented in Equation 2 summarizes how the net increment consumption calculation is performed under the PSDCREDIT option. Under this op tion, AERMOD first
models the A and B groups together, then models the B and C groups together, and finally computes the difference to obtain the desired re sult, i.e., the value to compare to the PSD
increment standard. In order for AERMOD to perform the special processing associated with this option, the user must define which sources belong to each of the groupings defined above. The next section describes how this is accomplished.58 2.6.6.3 Specifying Source Groups under the PSDCREDIT Option

The PSDCREDIT option introduces limitations on grouping sources in order to calculate increment consumption as described in the pr evious section. A new keyword, PSDGROUP, is used to group the sources to correctly calculate the increment consumption. The syntax, type, and order are similar to the regular SRCG ROUP keyword and are summarized below:

Syntax: SO PSDGROUP Grpid Srcid’s and/or Srcrng’s Type: Mandatory for PSDCREDIT option, Repeatable Order: Must follow the last keyword in the SO pathway before FINISHED

If the PSDCREDIT mode l option is specified, the PSDGROUP keyword must be used. The SRCGROUP keyword cannot be used under the PSDCREDIT option since results from other groupings beyond these three do not have any me aning when the PSDCREDIT option is invoked
and sources are allocated to the calculation of increment consumption. Special source groups for outputting model results are defined within AE RMOD for the PSDCREDIT option, as described
in the next section.

Only the following special PSD group ID’s can be used. Failure to use these group ID’s will result in a fatal error message during se tup processing by AERMOD. The group ID’s are:

INCRCONS – increment-c onsuming sources (group A above); these can be new sources or modifications to existing sources;
NONRBASE – existing, non-reti red baseline sources (group B above); and
RETRBASE – retired (increment-expanding or PSD credit) baseline sources (group C above).

It is important to note that the source emission inputs for sources included in the RETRBASE PSD group must be entered as positive numbers, unlike other types of PSD credit modeling where negative emissions are input to simulate the impact of the credit sources on the increment calculation. The increment-expanding contributi on from RETRBASE sources is accounted for
within the AERMOD model unde r the PSDCREDIT option.59 The group ID’s can appear in any order, but th ese are the only three th at can be specified. If there are no retired baseline sources (i.e., no baseline sources are retired), the keyword RETRBASE can be omitted. Likewise, if ther e are no non-retired baseline sources (i.e., all baseline sources have been retired), the NONRBASE keyword can be omitted. The special group ID ‘ALL’ that can be use with the S RCGROUP keyword cannot be used with the PSDGROUP keyword. As with the SRCGROUP keyword for non-PSDCREDIT applications, the group ID’s are repeatable and they must be the last keyword before FINISHED on the SO pathway when the PSDCREDIT option is specified.

Source ranges, which are described in more detail in Section 3.3.3 of the AERMOD User’s Guide (EPA, 2004a), are input as two source IDs separated by a dash, e.g., STACK1-
STACK10. Individual source IDs and source ranges may be used on the same card. If more than one input card is needed to define the s ources for a particular gr oup, then additional cards may be input, repeating the pa thway, keyword and group ID. A s ource can appear in only one of these source groups, and must be assigned to one of the groups.

The requirements for specifying sources and source groups under the PSDCREDIT option are summarized below:

 The SRCGROUP keyword cannot be used with the PSDCREDIT option;

 Special PSD group ID’s must be us ed with the PSDGROUP keyword;

 The group ID ALL is not allowed when the PSDCREDIT option is specified;

 A source must appear in one, and only one, of the PSDGROUPs; and

 Emission rates for increment-expanding (RETRBASE) sources must be entered as positive values.

2.6.6.4 Model Outputs under the PSDCREDIT Option

Unlike the regular SRCGROUP keyword, th e PSDGROUP keyword doe s not define how the source impacts are grouped for model output. As described in the previous sections, the PSDGROUP keyword defines the different categorie s of sources needed in order to properly
account for NO x conversion chemistry unde r the PVMRM option.60 The model outputs under the PSDCREDIT option in AERMOD are based on demonstrating compliance with the air quality standards, i.e., the NAAQS and PSD increment
for NO 2 . As a result, AERMOD uses hardc oded “SRCGROUP” names of ‘NAAQS’ and ‘PSDINC’ to label these two types of outputs. The results output under the ‘NAAQS’ source group label are based on the calculation of ( A + B ) as described above in Section 2.6.6.2. The results reported under the ‘PSD INC’ source group label are ba sed on the expression presented above in Equation 2.

2.7 VARIABLE EMISSION RATES

2.7.1 Specifying Variable Em ission Factors (EMISFACT)

The AERMOD model provides the option of specify ing variable emission rate factors for individual sources or for groups of sources. The syntax, type and order of the EMISFACT keyword are summarized below:

Syntax: SO EMISFACT SrcID or SrcRange Qflag Qfact(i), i=1,n Type: Optional, Repeatable Order: Must follow the LOCATION card for each source input

where the SrcID parameter is the same source ID that was entered on the LOCATION card for a particular source. The user also has the option of using the SrcRange parameter for specifying a range of sources for which the emission rate factor s apply, instead of identif ying a single source. This is accomplished by two source ID character strings se parated by a dash, e.g., STACK1- STACK10. The use of the SrcRange parameter is e xplained in more detail in the description of the BUILDHGT keyword (see Section 3.3.3 of the AERMOD User’s Guide).

The parameter Qflag is the variable emission ra te flag, and must be specified as one of the following secondary keywords (the number in parentheses indicates the number of values required for each option):61 SEASON - emission rates vary seasonally (n=4),

MONTH - emission rates vary monthly (n=12),

HROFDY - emission rates vary by hour-of-day (n=24),

WSPEED - emission rates vary by wind speed (n=6),

SEASHR - emission rates vary by season and hour-of-day (n=96),

HRDOW - emission rates vary by hour-of-da y, and day-of-week [M-F, Sat, Sun] (n=72),

HRDOW7 - emission rates vary by hour-of-day, and the seven days of the week [M, Tu, W, Th, F, Sat, Sun] (n=168),

SHRDOW - emission rates vary by season, hour-of-day, and day-of-week [M-F, Sat, Sun] (n=288),

SHRDOW7 - emission rates vary by season, hour-of-day, and the seven days of the week [M, Tu, W, Th, F, Sat, Sun] (n=672),

MHRDOW - emission rates vary by month, hour-of-day, and day-of-week [M-F, Sat, Sun] (n=864), and

MHRDOW7 - emission rates vary by month, hour-of-day, and the seven days of the week [M, Tu, W, Th, F, Sat, Sun] (n=2,016).

The Qfact array is the array of factors, wher e the number of factor s is shown above for each Qflag option. The seasons are defined in the following order: Winter (Dec., Jan., Feb.), Spring (Mar., Apr., May), Summer (Jun., Jul., Aug.) , and Fall (Sep., Oct., Nov.). The wind speed categories used with the WSPEED option may be defined using the ME WINDCATS keyword. If the WINDCATS keyword is not used, the de fault wind speed categories are defined by the upper bound of the first five categories as follows (the sixth category is assumed to have no upper bound): 1.54, 3.09, 5.14, 8.23, and 10.8 m/s. The EMISFACT card may be repeated as many times as necessary to input all of the fact ors, and repeat values may be used for the numerical inputs. Examples for the more re cent HRDOW and MHRDOW options are presented below, with column headers to indicate the order in which values are to be to input:62 SO EMISFACT STK1 HRDOW enter 24 hourly scalars for each of the “days”, first for Weekdays (Monday-Friday), then for Saturdays, and finally for Sundays, e.g., ** Weekdays: Hrs: 1-5 6 7-17 18 19-24
SO EMISFACT STK1 HRDOW 5*0.3 0.5 11*1.0 0.5 6*0.3 ** Saturdays: Hrs: 1-5 6 7-17 18 19-24
SO EMISFACT STK1 HRDOW 5*0.3 0.5 11*1.0 0.5 6*0.3 ** Sundays: Hrs: 1-5 6 7-17 18 19-24

SO EMISFACT STK1 HRDOW 5*0.3 0.5 11*1.0 0.5 6*0.3

SO EMISFACT STK1 HRDOW7 enter 24 hourly scalars for each of the “days”, first for Mondays, then for Tuesdays, ..., then for Saturdays, and finally for Sundays, e.g., ** Mondays: Hrs: 1-5 6 7-17 18 19-24
SO EMISFACT STK1 HRDOW7 5*0.3 0.5 11*1.0 0.5 6*0.3 ** Tuesdays: Hrs: 1-5 6 7-17 18 19-24
SO EMISFACT STK1 HRDOW7 5*0.3 0.5 11*1.0 0.5 6*0.3

.

.

. ** Saturdays: Hrs: 1-5 6 7-17 18 19-24
SO EMISFACT STK1 HRDOW7 5*0.3 0.5 11*1.0 0.5 6*0.3 ** Sundays: Hrs: 1-5 6 7-17 18 19-24
SO EMISFACT STK1 HRDOW7 5*0.3 0.5 11*1.0 0.5 6*0.3

SO EMISFACT STK1 MHRDOW enter 24 hourly scalars for each of the twelve months, first for Weekdays (Monday-Friday), then for Saturdays, and finally for Sundays, e.g., ** Weekdays JAN FEB MAR APR MAY JUN . . . NOV DEC
SO EMISFACT STK1 MHRDOW 24*1.0 24*0.8 24*0.6 24*0.8 24*1.0 24*0.8 24*0.6 24*0.8 ** Saturdays:
SO EMISFACT STK1 MHRDOW 24*1.0 24*0.8 24*0.6 24*0.8 24*1.0 24*0.8 24*0.6 24*0.8 ** Sundays:
SO EMISFACT STK1 MHRDOW 24*1.0 24*0.8 24*0.6 24*0.8 24*1.0 24*0.8 24*0.6 24*0.8

SO EMISFACT STK1 MHRDOW7 enter 24 hourly scalars for each of the twelve months, first for Mondays, then for Tuesdays, ..., then for Saturdays, and finally for Sundays, e.g., ** Mondays JAN FEB MAR APR MAY JUN . . . NOV DEC

SO EMISFACT STK1 MHRDOW7 24*1.0 24*0.8 24*0.6 24*0.8 24*1.0 24*0.8 24*0.6 24*0.8 ** Tuesdays JAN FEB MAR APR MAY JUN . . . NOV DEC
SO EMISFACT STK1 MHRDOW7 24*1.0 24*0.8 24*0.6 24*0.8 24*1.0 24*0.8 24*0.6 24*0.8

.

.

. ** Saturdays:

SO EMISFACT STK1 MHRDOW7 24*1.0 24*0.8 24*0.6 24*0.8 24*1.0 24*0.8 24*0.6 24*0.8 ** Sundays:
SO EMISFACT STK1 MHRDOW7 24*1.0 24*0.8 24*0.6 24*0.8 24*1.0 24*0.8 24*0.6 24*0.863 2.7.2 Specifying an Hourly Emi ssion Rate File (HOUREMIS)

The source (SO) pathway includes an option fo r inputting hourly emission rates for the AERMOD model, controlled by the HOUREMIS keyword. AERMOD currently allows for a single hourly emission file to be used with each model run. The syntax, type and order for this keyword are summarized below:

Syntax: SO HOUREMIS Emifil Srcid's (and/or Srcrng's) Type: Optional, Repeatable Order: Must follow the LOCATION card for each source input

where the Emifil parameter specifies the filena me for the hourly emission file, and Srcid or Srcrng identify the source or sources for whic h hourly emission rates are included. The Emifil filename can be up to 200 characters in length based on the default parameters in AERMOD. Double quotes (“) at the beginning a nd end of the filename can also be used as field delimiters to allow filenames with embedded sp aces. Source ranges, which are described in more detail in
Section 3.3.3 of the AERMOD User’s Guide (EPA, 2004a), are input as two source IDs separated by a dash, e.g., STACK1-STACK10. The user may include more than one HOUREMIS card in a runstream file, if needed to specify additional sources, but there can be only one hourly emissions file, and therefore th e filename must be th e same on all HOUREMIS
cards.

The format of each record of the hourly emissions file includes a pathway and keyword (SO HOUREMIS), followed by the Year, Month, Day, Hour, Source ID, and emission rate (in the appropriate units). For POIN T sources, the stack gas exit temp erature (K), and stack gas exit velocity (m/s) are also specified. Beginning with version 09292, the release heights and initial dispersion coefficients can also be vari ed on an hourly basis for AREA, AREAPOLY, AREACIRC, and VOLUME sources using the H OUREMIS option. The user selects this enhanced option by including the additional source parameters in the hourly emissions file. AERMOD determines whether hourly release heights and initial disp ersion coefficients are being64 used based on the first HOUREMIS record for each source, and these add itional parameters must
be included on all HOUREMIS r ecords unless the emissions are missing, which is indicated by leaving the emission rate and all fi elds beyond the source ID blank.

The hourly emissions file is processed using the same routines used to process the runstream input file, therefore each of the parameters must be separated by at least one space, but
otherwise the format is flexible. It is also not necessary to include the SO HOUREMIS on each line, as long as the parameters (Year, Month, etc.) do not begin be fore column 13. The data in the hourly emission file must also include th e exact same dates as are included in the meteorological input files, and the source IDs must correspond to the source IDs defined on the
SO LOCATION cards and be in the same order as defined in the ‘a ermod.inp’ file.

The model will check for a date mismatch between the hourly emissions file and the meteorological data, and also for a source ID mism atch. However, it is not necessary to process the entire hourly emissions file on each model run, i.e., the correct emissions data will be read if the ME DAYRANGE or the ME STARTEND cards (see Section 3.5.4 of the AERMOD User’s Guide) are used, as long as all the dates (includi ng those that are proce ssed and those that are skipped) match the meteorological data files.

An example of several lines from an hourly emissions file for two point sources is provided below:

The use of hourly varying releas e heights and initial dispersion coefficients for VOLUME and
AREA sources is illustrate d in the following example:

SO HOUREMIS 88 8 16 1 STACK1 52.5 382.60 12.27 SO HOUREMIS 88 8 16 1 STACK2 44.3 432.33 22.17 SO HOUREMIS 88 8 16 2 STACK1 22.3 377.88 9.27 SO HOUREMIS 88 8 16 2 STACK2 42.2 437.68 19.67 SO HOUREMIS 88 8 16 3 STACK1 51.5 373.72 11.87 SO HOUREMIS 88 8 16 3 STACK2 41.3 437.28 18.77 SO HOUREMIS 88 8 16 4 STACK1 36.0 374.83 9.63 SO HOUREMIS 88 8 16 4 STACK2 43.7 437.68 18.2365 For POINT sources, the mode l will use the stack release height and stack inside diameter defined on the SO SRCPARAM card, but will use the emi ssion rate, exit temperature and exit velocity from the hourly emission file. As noted above regarding VOLUME and AREA sources, if the emission rate, exit temperature and exit velocity are not included for a particular hour, i.e, any or all of those fields are blank, the model will inte rpret emissions data for that hour as missing and will set the parameters to zero. Since the emissi on rate will be zero, there will be no calculations
made for that hour and that source.

2.8 OUTPUT OPTIONS

A number of enhancements have been inco rporated in AERMOD, beginning with version 11059, to more fully support the form of the new 1-hour NO 2 and SO 2 standards, as well as the 24-hour PM2.5 standard. The form of these NAAQS are similar in that they are based on a ranked percentile value averaged over the number of years proc essed. In order to support implementation of recent guidance regarding m odeling to demonstrate compliance with these NAAQS, the RECTABLE keyword had been modifiedto allow user-specified ranks of shortterm averages (for all pollutants) up to the 999th highest value. Th e previous version of
AERMOD was limited to the 10th -highest value and also rest ricted the rank for the 24-hour PM2.5 NAAQS to the 8th highest value (correspo nding to the 98th percent ile of daily values during a year).

2.8.1 Output Options for 24-hour PM2.5 and 1-hour NO 2 and SO 2 Standards

Beginning with version 11059, thre e output options have been incorporated on the OU pathway to support the 1-hour NO 2 and SO 2 standards, especially the analyses that may be required to determine a source’s (or group of sources ) contributions to modeled violations of the

SO HOUREMIS 88 3 1 1 VOL1 500.0 2.0 2.0 2.0 SO HOUREMIS 88 3 1 1 AREA1 5.000 2.0 2.0 SO HOUREMIS 88 3 1 2 VOL1 500.0 2.0 2.0 3.0 SO HOUREMIS 88 3 1 2 AREA1 5.000 2.0 3.0 SO HOUREMIS 88 3 1 3 VOL1 500.0 2.0 2.0 4.0 SO HOUREMIS 88 3 1 3 AREA1 5.000 2.0 4.066 NAAQS for comparison to the Significant Impact Le vel (SIL). The form of the standards, based on averages of ranked values acro ss years, complicates this anal ysis, especially for the 1-hour
NO 2 and SO 2 standards which are based on ranked va lues from the distribution of daily maximum 1-hour averages. One of the options (MAXDCONT) can also be used for the 24-hour PM2.5 NAAQS.

The MAXDCONT option, applicab le to 24-hour PM2.5, 1-hour NO 2 and 1-hour SO 2 standards, can be used to determine the contri bution of each user-defined source group to the high ranked values for a target s ource group, paired in time and space. This is accomplished as an internal post-processing routine after the main model run is completed. The user can specify the range of ranks to analyze, or can specify an upper bound rank, e.g., 8th-highest for 1-hour
NO 2 (note that “upper bound” rank implies a high er concentration, whil e “lower bound” rank implies a lower concentration), and a threshold value, such as the NAAQS, for the target source group. The model will process each rank within th e range specified, but will stop after the first rank (in descending order of concentrati on) that is below the threshold.

The syntax, type and order of the opt ional MAXDCONT keyword are summarized
below:

Syntax: OU MAXDCONT GrpID UpperRank LowerRank FileName (FileUnit)

or OU MAXDCONT GrpID UpperRank THRESH ThreshValue FileName (FileUnit) Type: Optional, Repeatable

where GrpID is the target or reference sour ce group toward which c ontributions are being determined, UpperRank and LowerRank are the upper bound and lower bound ranks (where upper bound rank implies higher concentrations and lowe r bound rank implies lower concentrations), THRESH indicates that the lower bound rank is determined based on a lower concentration threshold, ThreshValue is the use r-specified concentrati on threshold for GrpID impacts which serves as a lower bound on the range of ranks analyzed, FileName is the output file name, and (FileUnit) is the optional file unit. Th e filename can be up to 200 characters in length based on the default parameters in AERM OD. Double quotes (“) at the beginning and67 end of the filename can also be used as fiel d delimiters to allow filenames with embedded spaces. When the THRESH option is selected AERMOD will sk ip the contribution analysis for any receptor where the target GrpID impact is less than the threshold, and will stop processing completely after the first rank where the target GrpID values are below the threshold for all receptors. NOTE: It is important note that the range of ranks that can be analyzed under the MAXDCONT option is limited to the ra nge of ranks (not the individual ranks) specified on the OU RECTABLE keyword, even when the THRESH option is used in lieu of specifying a LowerRank value. AERMOD will issue a fatal error if the THRESH option is used and the range of ranks is less than or equal to 8 for the 1-hr SO2 NAAQS, or less than or equal to 12 for the 1-hr NO2 and 24-hr PM2.5 NAAQS. Non-fatal warning messages will be generated if the THRESH option is used and the range of ranks is less than or equal to 24 for the 1-hr SO2 NAAQS, or less than or equal to 28 for the 1-hr NO2 and 24-hr PM2.5 NAAQS.

When the MAXDCONT option is specifi ed, AERMOD stores all meteorological variables in memory for each hour during the initia l stage of processing in order to optimize the model runtime during the post-processing stage. Any temporally-varying emissions and background concentrations, incl uding background ozone concen trations for the OLM and PVMRM options, are also stored in memory for each hour. Wh ile optimizing runtime for the post-processing, this approach may also significantly in crease the memory storage requirements of the model. In addition, since the MAXDCO NT option extracts meteorological variables and other temporally-varying data stored in memo ry to optimize runtime, the MAXDCONT option
cannot be used with the mode l “re-start” option using the INITFILE and SAVEFILE keywords on the CO pathway, or with the MU LTYEAR option on the CO pathway.

The MAXDAILY option, introduced with ve rsion 11059, is applicable to 1-hour NO 2 and
1-hour SO 2 NAAQS and generates a file of daily maximum 1-hour conc entrations for a specified source group, for each day in the data period processed. The MAXDAILY file provides an interim output that may be usef ul for analyzing the 1-hour NO 2 and SO 2 NAAQS. The syntax, type and order of the optional MAXDAI LY keyword are summarized below:68 Syntax: OU MAXDAILY GrpID FileName (FileUnit) Type: Optional, Non-repeatable

where GrpID is the source group selected for da ily maximum 1-hour values, FileName is the name of the MAXDAILY output file , and FileUnit is the optional file unit. The filename can be up to 200 characters in length based on the defa ult parameters in AERMOD. Double quotes (“) at the beginning and end of the filename can also be used as field delimiters to allow filenames with embedded spaces.

Another option applicable to 1-hour NO 2 and 1-hour SO 2 NAAQS introduced with version 11059, the MXDYBYYR keyword, genera tes a summary of daily maximum 1-hour concentrations by year for each rank specified on the RECTABLE keyword. The data periods included in the MXDYBYYR file are the peri ods used in the MAXDCONT postprocessing option. The syntax, type and order of the optional MXDYBYYR keyword are summarized
below:

Syntax: OU MXDYBYYR GrpID FileName (FileUnit) Type: Optional, Non-repeatable

where GrpID is the source group selected for da ily maximum 1-hour values summarized by year, FileName is the name of the MXDYBYYR output file , and FileUnit is the op tional file unit. The filename can be up to 200 characters in length based on the default parameters in AERMOD. Double quotes (“) at the beginning a nd end of the filename can also be used as field delimiters to
allow filenames with embedded spaces.

2.8.2 Miscellaneous Output Options

The optional SUMMFILE keyword can be used to generate a separate formatted output file containing the summary of high ranked va lues included at the end of the standard ‘aermod.out’ file. The optional FILEFORM keyw ord can be used to specify the use of exponential notation, rather than fixed format as currently used, for results that are output to69 separate result files. The opti onal NOHEADER keyword can be used to suppress file headers in formatted output file options. Thes e new options are described below.

The syntax, type and order of the optiona l SUMMFILE keyword are summarized below:

Syntax: OU SUMMFILE SummFileName Type: Optional, Non-repeatable

where the SummFileName is the name of the external file containing the summary of high
ranked values. The SUMMFILE filename can be up to 200 characters in length based on the default parameters in AERMOD. Double quotes (“ ) at the beginning and end of the filename can
also be used as field delimiters to allow f ilenames with embedded spaces. In addition to the summary of high ranked values, the SUMMFI LE also includes the “MODEL SETUP OPTIONS SUMMARY” page from the main ‘aermod.out’ file.

The syntax, type and order of the optiona l FILEFORM keyword are summarized below:

Syntax: OU FILEFORM EXP or FIX Type: Optional, Non-repeatable

where the EXP parameter specifies that output resu lts files will use exponential-formatted values, and the FIX parameter specifies that the output results files will use fixed-formatted values. The default option is to use fixed-form atted results, so use of FILEFORM = ‘FIX’ is extraneous. Note that AERMOD only examines th e first three characters of the input field, so
that the full terms of ‘EXPONEN TIAL’ or ‘FIXED’ can also be used. The format specified on this optional keyword is applicable to PL OTFILEs, plot-formatted POSTFILEs, MAXIFILEs, RANKFILEs, and SEASONHR files, but will not aff ect the format of results in the standard ‘aermod.out’ file or the optional SUMMFILE. The FILEFORM optional may be useful to preserve precision in applications with relativ ely small impacts, especially for the purpose of post-processing hourly concentrations using th e POSTFILE option. The option may also be useful for applications with relatively large impacts that may overflow the Fortran format70 specifier of F13.5 used for fixed-formatted out puts. AERMOD will issue a warning message if values that exceed the range allowed for fixe d-format are detected unless the FILEFORM EXP option has been selected.

The syntax, type and order of the opti onal NOHEADER keyword are summarized below:

Syntax: OU NOHEADER FileType1 FileType2 FileType3 ... FileTypeN

or OU NOHEADER ALL Type: Optional, Non-repeatable

where FileTypeN identifies the keywords for form atted output files for which the file headers will be suppressed, which may include the includes the following file types: POSTFILE, PLOTFILE, MAXIFILE, RANKFILE, SE ASONHR, MAXDAILY, MXDYBYYR, and MAXDCONT. The keyword ALL may be used to specify that h eader records will be suppressed for ALL applicable output file types.

2.9 MODEL STORAGE LIMITS

The AERMOD model has been designed usi ng a dynamic storage allocation approach, where the model allocates data storage as need ed based on the number of sources, receptors, source groups, and input requirements, up to th e maximum amount of memory available on the computer being used. The AERMOD model uses dynamic arrays to allocate data storage at model runtime rather than at compile time. The AERMOD model preprocesses the model runstream input file to determine the data stor age requirements for a particular model run, and then allocates the input data arrays before pro cessing the setup data. Once the setup processing is completed, the model allocates storage for the result arrays. When allocating data storage, the AERMOD model traps for errors, e.g., not enough memory available to allocate. If the allocation is unsuccessful, then an error message is ge nerated by the model and further processing is prevented. If the CO RUNORNOT NOT option is selected, the model wi ll still go through all array allocations so that the user can determine if sufficient memory is available to complete the71 run. Also, an estimate of the total amount of memory needed for a particular run is printed out as part of the first page of printed output.

The storage parameters that are established at model runtime are as follows:

NSRC = Number of Sources NREC = Number of Receptors NGRP = Number of Source Groups NOLM = Number of OLM Gr oups (OLMGROUP Keyword) NAVE = Number of Short Term Averaging Periods NVAL = Number of High Values by Receptor (RECTABLE Keyword) NTYP = Number of Output Types (C ONC currently is th e only output type) NMAX = Number of Overall Maxi mum Values (MAXTABLE Keyword) NQF = Number of Variable Em ission Rate Factors per Source NPDMAX = Number of Particle Diameter Categories per Source NVMAX = Number of Vertices for Area Sources (including AR EA, AREACIRC, and AREAPOLY source types) and/or OPENPIT Sources NSEC = Number of Sectors for Buildi ng Downwash Parameters (set to 36 if downwash sources are included) NURB = Number of Urban Areas (URBANOPT Keyword) NNET = Number of Cartesian an d/or Polar Receptor Networks IXM = Number of X-coord (Distance) Values per Receptor Network IYM = Number of Y-coord (Direct ion) Values per Receptor Network NARC = Number of Receptor Arcs Used with EVALCART Keyword NEVE = Number of Events for EVENT processing

The MAXDCONT option on the OU pathway introduced with version 11059 to determine source group contributions to modele d values under the 24-hr PM2.5 and 1-hr SO2 and NO2 NAAQS can significantly increase the memory requirements of AERMOD due to the fact that all meteorological a nd other variables needed to perform the MAXDCONT processing are stored in memory in orde r to optimize model runtime. Th e memory requirements for the72 MAXDCONT have been optimized with version 12060, and a new option on the ME pathway
was also introduced with versi on 12060 to further reduce memory requirements for applications involving less than five (5) years of meteorological data, e.g., ifone or more years of sitespecific meteorological data area being used. The NUMYEARS keyword on the ME pathway allows the user to specify the number of years of data being processed for purposes of allocating array storage for the MAXDCONT option, with a default value of five (5) years being assumed if the optional NUMYEARS keyword is omitted. The syntax of the optional NUMYEARS keyword is summarized below:

Syntax: ME NUMYEARS NumYrs Type: Optional, Non-repeatable

where NumYrs specifies the number of (full) ye ars of meteorological data being processed.73 3.0 REFERENCES

Cimorelli, A. J., S. G. Perry, A. Venkatram, J. C. Weil, R. J. Paine, R. B. Wilson, R. F. Lee, W. D. Peters, R. W. Brode, and J. O. Paumie r, 2004: AERMOD: Description of Model Formulation. EPA 454/R-03-004. U. S. Environm ental Protection Agency, Research Triangle Park, North Carolina 27711.

EPA, 1995a: User = s Guide for the Industrial Source Complex (ISC3) Dispersion Models, Volume I - User Instructions. EPA-454/B-95-00 3a. U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711.

EPA, 1995b: User = s Guide for the Industrial Source Complex (ISC3) Dispersion Models, Volume II - Description of Model Algorith ms. EPA-454/B-95-003b. U.S. Environmental Protection Agency, Research Tr iangle Park, North Carolina 27711.
EPA, 2000. Meteorological Mon itoring Guidance for Regulatory Modeling Applications. EPA454/R-99-005. Office of Air Qual ity Planning & Standards, Res earch Triangle Park, NC. (PB 2001-103606)
EPA, 2003: AERMOD Deposition Algorithms - Sc ience Document (Revised Draft). U.S. Environmental Protection Agency, Res earch Triangle Park, North Carolina 27711.

EPA, 2004a: User = s Guide for the AMS/EPA Regulatory Model - AERMOD. EPA454/B-03-001. U.S. Environmental Protection Agenc y, Research Triangle Park, North Carolina 27711.
EPA, 2004b: User = s Guide for the AERMOD Meteorologi cal Processor (AERMET). EPA454/B-03-002. U.S. Environmental Protection Agen cy, Research Triangle Park, North Carolina 27711.
EPA, 2008: Risk and Exposure Assessment to Support the Review of the NO 2 Primary National Ambient Air Quality Standard. EPA-452/R-08-0 08a. U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711.
EPA, 2010a: Modeling Procedures for De monstrating Compliance with PM2.5 NAAQS. Stephen D. Page Memorandum, dated March 23, 2010. U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711.
EPA, 2010b: Applicability of Appendi x W Modeling Guidance for the 1-hour NO 2 National Ambient Air Quality Standard. Tyler Fox Memorandum, dated June 28, 2010. U.S. Environmental Protection Agency, Resear ch Triangle Park, North Carolina 27711.
EPA, 2010c: Applicability of Appendi x W Modeling Guidance for the 1-hour SO 2 National Ambient Air Quality Standard. Tyler Fox Memorandum, dated August 23, 2010. U.S. Environmental Protection Agency, Resear ch Triangle Park, North Carolina 27711.74 EPA, 2011: Additional Clarification Rega rding Application of Appendix W Modeling Guidance for the 1-hour NO 2 National Ambient Air Quality St andard. Tyler Fox Memorandum, dated March 1, 2011. U.S. Environmental Protec tion Agency, Research Triangle Park, North Carolina 27711.
Hanrahan, P.L., 1999a. "The plume volume molar ratio method for determining NO 2 /NO x ratios in modeling. Part I: Methodology," J. Air & Waste Manage. Assoc. , 49 , 1324-1331.
Hanrahan, P.L., 1999b. "The plume volume molar ratio method for determining NO 2 /NO x ratios in modeling. Part II: Evaluation Studies," J. Air & Waste Manage. Assoc. , 49 , 1332-1338.
Qian, W., and A. Venkatram, 2011: "Performance of Steady-State Dispersion Models Under Low Wind-Speed Conditions", Boundary Layer Meteorology , 138 , 475-491.
Walcek, C., G. Stensland, L. Zhang, H. Huang, J. Hales, C. Sweet, W. Massman, A. Williams, J, Dicke, 2001: Scientific Pee r-Review of the Report "Deposition Parameterization for the Industrial Source Complex (ISC3) Model." Th e KEVRIC Company, Durham, North Carolina.
Wesely, M.L, P.V. Doskey, and J.D. Shannon, 2002: Deposition Parameterizations for the Industrial Source Complex (ISC3) Mode l. Draft ANL report ANL/ER/TR

B 01/003, DOE/xxnnnn, Argonne National Laborat ory, Argonne, Illinois 60439.

Note: All references listed here, with the exception of Hanr ahan (1999a and 1999b), Qian and Venkatram (2011) and EPA (2008), can be found on the U.S. EPA SCRAM website at the following url: http://www.epa.gov/scram001/A-1 

### APPENDIX A. ALPHABET ICAL KEYWORD REFERENCE

This appendix provides an alphabetical list ing of all of the keywords used by the AERMOD model. Each keyword is identified as to the pathway for which it applies, the keyword type (either mandatory or optional, and e ither repeatable or non-r epeatable), and with a brief description of the functi on of the keyword. For a more complete description of the keywords, including a list of associated paramete rs, refer to Section 2.0 of this Addendum, the Functional Keyword/Parameter Reference in Appendi x B of this Addendum, and/or the Detailed Keyword Reference in Section 3 of the AERMOD User’s Guide (EPA, 2004a).A-2 Keyword Path Type Keyword Description
AREAVERT SO M – R Specifies location of vertices for an AREAPOLY source type (mandatory if AREAPOLY source is used)
AVERTIME CO M – N Averaging time(s) to process
BACKGRND SO O – R Option to specify temporally varying background concentrations
BACKUNIT SO O – N Option to specify units for background concentrations
BUILDHGT SO O – R Building height values for each wind sector
BUILDLEN SO O – R Building projected length values for each wind sector
BUILDWID SO O – R Building projected width values for each wind sector
CONCUNIT CO O – N Optional conversion factors for emission input units and concentration output units
DAYRANGE ME O – R Specifies days or ranges of days to process (default is to process all data)
DAYTABLE OU O – N Option to provide summaries for each averaging period for each day processed.
DCAYCOEF CO O – N Optional decay coefficient for exponential decay
DEBUGOPT CO O – N Option to generate detailed r esult and meteorology files for debugging purposes
DEPOUNIT SO O – N Optional conversion factors for emission input units and deposition output units
DISCCART RE O – R Defines discretely placed receptors referenced to a Cartesian system DISCPOLR RE O – R Defines discretely placed receptors referenced to a polar system
ELEVUNIT SO RE O – N O – N Defines input units for receptor elevations (RE path), or source elevations (SO path) (defaults to meters)
EMISFACT SO O – R Optional input for variable emission rate factors
EMISUNIT SO O – N Optional conversion factors for emission units and concentration units
ERRORFIL CO O – N Option to generate detailed error lis ting file (error file is mandatory for CO RUNORNOT NOT case)
EVALCART RE O – R Defines discretely placed receptor locations referenced to a Cartesian system, grouped by arc for use with the EVALFILE output option
EVALFILE OU O – R Option to output file of normalized arc maxima for model evaluation studies
EVENTFIL CO O – N Specifies whether to generate an input file for EVENT model
EVENTLOC EV M – R Describes receptor location for an eventA-3 Keyword Path Type Keyword Description
EVENTOUT OU M – N Specifies level of output information provided by the EVENT model
EVENTPER EV M – R Describes data and averaging period for an event
FILEFORM OU O – N Specify fixed or exponential format for output results files
FINISHED ALL M – N Identifies the end of inputs for a particular pathway
FLAGPOLE CO O – N Specifies whether to accept receptor heights above local terrain (m) for use with flagpole receptors, and allows for a default flagpole height to be specified
GASDEPDF CO O – N Option to override default parameters for gas dry deposition
GASDEPOS SO O – R Specify source parameters for gas deposition algorithms
GASDEPVD CO O – N Option to specify deposition velocity for gas dry deposition
GDLANUSE CO O – N Specify land use categories by sector for gas dry deposition
GDSEASON CO O – N Specify seasonal definitions for gas dry deposition
GRIDCART RE O – R Defines a Cartesian grid receptor network
GRIDPOLR RE O – R Defines a polar receptor network
HALFLIFE CO O – N Optional half-life for exponential decay
HOUREMIS SO O – R Option for specifying hourly emission rates in a separate file
INCLUDED SO, RE, EV O – R Option to include input data from a separate file in the runstream for the SO and/or RE pathways, or for the EV pathway for EVENTs
INITFILE CO O – N Option to initialize model from file of intermediate results generated by SAVEFILE option
LOCATION SO M – R Identifies coordinates for particular source location LOW_WIND CO O – N Option for user-specified para meters for the LOWWIND1 and LOWWIND2 BETA options
MASSFRAX SO O – R Optional input of mass fraction for each particle size category
MAXDAILY OU O – R Option to output file of daily maximum 1-hour values for each day processed; only applicable for 1-hour NO 2 and 1-hour SO 2 NAAQS
MAXDCONT OU O – R Option to output cont ributions of each s ource group to ranked values averaged across years for a reference source group, paired in time and space; only applicable for 24-hour PM2.5, 1-hour NO 2 , and 1-hour SO 2 NAAQS
MAXIFILE OU O – R Option to list events exceeding a threshold value to file (if CO EVENTFIL option is used, these events are included in the input file generated for the EVENT model)
MAXTABLE OU O – R Option to summarize the overall maximum values METHOD_2 SO O – R Specify optional source parameters for METHOD_2 option for particle depositionA-4 Keyword Path Type Keyword Description
MODELOPT CO M – N Job control and dispersion options
MULTYEAR CO O – N Specifies that run is part of a multi-year run, e.g., for PM-10 H6H in five years
MXDYBYYR OU O – R Option to output file of daily maximum 1-hour values by year, for each year processed; only applicable for 1-hour NO 2 and 1-hour SO 2 NAAQS
NOHEADER OU O – N Option to suppress file headers for output file options, e.g., POSTFILE, PLOTFILE, MAXDCONT, etc NO2EQUIL CO O – N Option to override default NO 2 /NO x equilibrium ratio for PVMRM or OLM
NO2RATIO SO O – R Option to specify in-stack NO 2 /NO x equilibrium ratio for OLM and PVMRM options by source
NO2STACK CO O – N Option to specify default in-stack NO 2 /NO x equilibrium ratio for OLM and PVMRM options; may be overridden by NO2RATIO
NUMYEARS ME O – N Option to specify the number of years of meteorological data being processed for purposes of allocating array storage for the OU MAXDCONT option
OLMGROUP SO O – R Specifies sources to combine for OLM option for merging plumes
OZONEFIL CO O – N Specifies hourly ozone file for OLM and PVMRM options
OZONEVAL CO O – N Specifies background value of ozone for OLM and PVMRM options
OZONUNIT CO O – N Option to specify units for temporally-varying ozone concentrations for the O3VALUES keyword.
O3VALUES CO O – R Option to specify temporally varying ozone concentrations for use with OLM and PVMRM options for estimating NO 2 PARTDENS SO O – R Specifies particle density by si ze category for particle deposition
PARTDIAM SO O – R Specifies particle diameters by size category for particle deposition
PLOTFILE OU O – R Option to write certain results to a storage file suitable for input to plotting routines
POLLUTID CO M – N Identifies pollutant being modeled
POSTFILE OU O – R Option to write results to a ma ss storage file for postprocessing
PROFBASE ME M – N Specifies the base elevation for the potential temperature profile
PROFFILE ME M – N Describes input profile meteorological data file
PSDGROUP SO O – R Specifies source groups for PSDCREDIT option with PVMRM
RANKFILE OU O – R Option to produce output file of ranked values for Q-Q plots
RECTABLE OU O – R Option to output high rank ed value(s) by receptor
RUNORNOT CO M – N Identifies whether to run model or process setup information onlyA-5 Keyword Path Type Keyword Description
SAVEFILE CO O – N Option to store intermediate results for later restart of the model after user or system interrupt
SCIMBYHR ME O – N Specifies sampling parameters for the SCIM option
SEASONHR OU O – R Option to output values by season and hour-of-day
SITEDATA ME O – N Describes on-site meteorological station
SRCGROUP SO M – R Identification of source groups
SRCPARAM SO M – R Identifies source parameters for a particular source
STARTEND ME O – N Specifies start and end dates to be read from input meteorological data file (default is to read entire file)
STARTING ALL M – N Identifies the start of inputs for a particular pathway
SUMMFILE OU O – N Option to output summary of high ranked values to separate file
SURFDATA ME M – N Surface meteorological station
SURFFILE ME M – N Describes input surface meteorological data file
TITLEONE CO M – N First line of title for output
TITLETWO CO O – N Optional second line of output title
TOXXFILE OU O – R Creates output file for use with TOXX model component of TOXST
UAIRDATA ME M – N Upper air meteorological station
URBANOPT CO O – R Option to specify population for urban option
URBANSRC SO O – R Option to specify use of urban option by source
WDROTATE ME O – N Wind direction rotation adjustment
WINDCATS ME O – N Upper bound of wind speed categories
XBADJ SO O – R Along-flow distances from the stack to the center of the upwind face of the projected building
YBADJ SO O – R Across-flow distances from the stack to the center of the upwind face of the projected buildingB-1 

### APPENDIX B. FUNCTIONAL KEYWORD/PARAMETER REFERENCE

This appendix provides a functional referen ce for the keywords and parameters used by the input runstream files for the AERMOD model. The keywords are organized by functional pathway, and within each pathway the order of the keywords is based on the function of the keyword within the preprocessor. The pathways used by the preprocessor are as follows, in the order in which they appear in the runstream file and in the tables that follow:

CO - for specifying overall job CO ntrol options; and SO - for specifying SO urce location information (optional); RE - for specifying RE ceptor information; and ME - for specifying ME teorology information and options; EV - for specifying EV ent information and options; OU - for specifying OU tput file information.

The pathways and keywords are presented in the same order as in the Detailed Keyword
Reference in Section 3 of the AERMOD User’s Guide (EPA, 2004a), and in the Quick Reference at the end of the manual, with the exception of new keywords that ar e not reflected in the original user’s guide.

Two types of tables are provided for each pa thway. The first table lists all of the keywords for that pathway, identifies each keywor d as to its type (either mandatory or optional and either repeatable or non-repe atable), and provides a brief de scription of the function of the keyword. The second type of table presents the parameters for each keyword, in the order in which they should appear in the runstream file where order is important, and describes each parameter in detail.

The following convention is used for identifying the different types of input parameters. Parameters corresponding to secondary keywords wh ich should be input "a s is" are listed on the tables with all capital letter s and are underlined, although none of the inputs to AERMOD are
treated as case-sensitive. Other parameter names are given with an initial capital letter and are not input "as is." In a ll cases, the parameter names are intend ed to be descriptive of the input variable being represented, and th ey often correspond to the Fortra n variable names used in theB-2 AERMOD code. Parentheses around a parameter i ndicate that the parameter is optional for that keyword. The default that is taken when an optio nal parameter is left blank is explained in the discussion for that parameter.B-3 TABLE B-1
DESCRIPTION OF CONTRO L PATHWAY KEYWORDS

CO Keywords Type Keyword Description
STARTING M – N Identifies the start of CONTROL pathway inputs
TITLEONE M – N First line of title for output
TITLETWO O – N Optional second line of title for output
MODELOPT M – N Job control and dispersion options
AVERTIME M – N Averaging time(s) to process
URBANOPT O – R Specifies parameters for urban dispersion option
POLLUTID M – N Identifies type of pollutant being modeled
HALFLIFE 1 O – N Optional half life used for exponential decay
DCAYCOEF 1 O – N Optional decay coefficient
GASDEPDF O – N Option to override default parameters for gas dry deposition
GASDEPVD O – N Option to specify deposition velocity for gas dry deposition
GDLANUSE O – N Specify land use categories by sector for gas dry deposition
GDSEASON O – N Specify seasonal definitions for gas dry deposition LOW_WIND O – N Option for user-specified parameters for the LOWWIND1 and LOWWIND2 BETA options NO2EQUIL O – N Option to override default NO 2 /NO x equilibrium ratio for PVMRM or OLM
NO2STACK O – N Option to specify default in-stack NO 2 /NO x equilibrium ratio for OLM and PVMRM options; may be overridden by NO2RATIO option on SO pathway
OZONEFIL O – N Specifies filename for hourly ozone file for use with OLM and PVMRM options
OZONEVAL O – N Specifies background value of ozone for use with OLM and PVMRM options
O3VALUES O – R Option to specify temporally varying ozone concentrations for use with OLM and PVMRM options for estimating NO 2 OZONUNIT O – N Option to specify units for temporally-v arying ozone concentrations for the O3VALUES keyword
FLAGPOLE O – N Specifies whether to accept receptor heights above local terrain (m) for use with flagpole receptors, and allows for default flagpole height to be specified
RUNORNOT M – N Identifies whether to run model or process setup information only
EVENTFIL 2 O – N Specifies whether to generate an input file for EVENT model
SAVEFILE 3 O – N Option to store intermediate results for rest art of model after user or system interrupt
INITFILE 3 O – N Option to initialize model from intermed iate results generated by SAVEFILE option
MULTYEAR 3 O – N Option to process multiple years of meteorological data (one year per run) andB-4 accumulate high short term values across years
DEBUGOPT O – N Option to generate detailed result and meteorology files for debugging purposes
ERRORFIL O – N Option to generate detailed error listing file
FINISHED M – N Identifies the end of CONTROL pathway inputs

Type: M – Mandatory N – Non-Repeatable O – Optional R – Repeatable

1) Either HALFLIFE or DCAYCOEF may be specified. If both cards appear a warning message will be issued and the first value entered will be used in calculations. The DFAULT option assumes a half life of 4 hours for SO 2 modeled in urban mode.

2) The EVENTFIL keyword controls whether or not to generate an input file for EVENT processing. The primary difference between AERMOD “regular” processing and EVENT processing by AERMOD is in the treatment of source group contributions. The AERMOD model treats the source groups independently, whereas EVENT processing determines individual source contributions to particular events, such as the design concentrations determined from AERMOD, or user-specified events. By specifying the EVENTFIL keyword, an input runstream file will be generated that can be used directly for EVENT processing. The events included in the generated EVENT processing input file are defined by the RECTABLE and MAXIFILE keywords on the OU pathway, and are placed in the EVent pathway.

3) The SAVEFILE and INITFILE keywords work together to implement the model's re-start capabilities. Since the MULTYEAR option utilizes the re-start features in a special way to accumulate high short term values from year to year, it cannot be used together with the SAVEFILE or INITFILE keyword in the same model run.B-5 TABLE B-2
DESCRIPTION OF CONTROL PATH WAY KEYWORDS AND PARAMETERS

Keyword Parameters

TITLEONE Title1
where: Title1 First line of title for output, character string of up to 68 characters (additional characters can be included on the TITLEONE keyword, but only the first 68 characters are printed in the output files).
TITLETWO Title2
where: Title2 Optional second line of title for output, character string of up to 68 characters (any additional characters are not printed)
MODELOPT DFAULT BETA CONC AREADPLT FLAT NOSTD NOCHKD NOWARN SCREEN SCIM PVMRM PSDCREDIT DEPOS and/or or or DDEP ELEV WARNCHKD OLM and/or WDEP

FASTALL DRYDPLT WETDPLT URBTRANS LOWWIND1 VECTORWS

or or or or FASTAREA NODRYDPLT NOWETDPLT LOWWIND2
where: DFAULT

BETA

CONC DEPOS DDEP WDEP AREADPLT

FLAT ELEV

NOSTD NOCHKD

WARNCHKD

NOWARN Specifies that regulatory default options will be used; specification of DFAULT option will override non-DFAULT options that may be specified Non-DFAULT option that allows for draft, “Beta” test options to be used; includes PSDCREDIT option and capped and horizontal stack releases Specifies that concentration values will be calculated Specifies that total deposition flux values will be calculated Specifies that dry deposition flux values will be calculated Specifies that wet deposition flux values will be calculated Specifies use of non-DFAULT method for optimized plume depletion due to dry removal mechanisms for area sources Non-DFAULT option of assuming flat terrain will be used Default option of assuming elevated terrain will be used;

Note : Both FLAT and ELEV may be specified in the same model run to allow specifying the non-DFAULT FLAT terrain option on a source-by-source basis (see the SO LOCATION keyword for specifying FLAT sources) Non-DFAULT option of no stack-tip downwash will be used Non-DFAULT option of suspending date checking will be used for non-sequential meteorological data files, also implemented when SCREEN option is specified Specifies option for issuing warning me ssages rather than fatal errors for non-sequential meteorological data files Option to suppress detailed listing of warning messages in the mainB-6 Keyword Parameters

SCREEN

SCIM

PVMRM

OLM

PSDCREDIT

FASTALL

FASTAREA

DRYDPLT

NODRYDPLT WETDPLT

NOWETDPLT NOURBTRAN

LOWWIND1

LOWWIND2

VECTORWS output file will be used Non-DFAULT option for running AERMOD in a screening mode for AERSCREEN will be used Non-DFAULT Sampled Chronological Input Model (SCIM) option; applies to ANNUAL averages only; SCIM sampling parameters must be specified on the ME pathway Non-DFAULT Plume Volume Molar Ratio Method (PVMRM) for NO 2 conversion will be used Non-DFAULT Ozone Limiting Method (OLM) for NO 2 conversion will be used Non-DFAULT BETA test option to calculate the increment consumption with PSD credits using the PVMRM option Non-DFAULT option to optimize model runtime for POINT, VOLUME and AREA sources (AREA optimizations formerly associated with TOXICS option) Non-DFAULT option to optimize m odel runtime for AREA sources (formerly associated with TOXICS option) Option to incorporate dry depletion (removal) processes associated with dry deposition algorithms; dry depletion will be used by default if dry deposition algorithms are invoked Option to disable dry depletion (removal) processes Option to incorporate wet depletion (removal) processes associated with wet deposition algorithms; wet depletion will be used by default if wet deposition algorithms are invoked Option to disable wet depletion (removal) processes. Non-DFAULT option to revert to the urban option as implemented prior to version 11059 (see Section 2.1.1). Non-DFAULT BETA option to addr ess concerns regarding model performance under low wind speed conditions (see Section 2.1.10). Cannot be used with LOWWIND2 option. Non-DFAULT BETA option to addr ess concerns regarding model performance under low wind speed conditions (see Section 2.1.10). Cannot be used with LOWWIND1 option. Option to specify that input wi nd speeds are vector mean (or resultant) wind speeds, rather than scalar means (see Section 2.1.2). The VECTORWS option is not linked with the DFAULT option.
AVERTIME Time1 Time2 . . . TimeN MONTH PERIOD

or ANNUAL
where: TimeN MONTH PERIOD Nth optional averaging time (1 , 2 , 3 , 4 , 6 , 8 , 12 , or 24 -hr) Option to calculate MONTH ly averages Option to calculate averages for the entire data PERIOD ; for the

MULTYEAR option, the summary of highest PERIOD averages is based on the highest PERIOD average across the individual years processed with MULTYEARB-7 Keyword Parameters
ANNUAL Option to calculate ANNUAL averages (assumes complete years); for multi-year meteorological data files, with and without the MULTYEAR option, the multi-year average of the ANNUAL values is reported URBANOPT For multiple urban areas: UrbanID Urbpop (Urbname) (UrbRoughness)
For single urban areas: Urbpop (Urbname) (UrbRoughness)
where: UrbanID UrbPop (UrbName) (UrbRoughness) Specifies the alphanumeric urban ID (up to eight characters) Specifies the population of the urban area Specifies the name of the urban area (optional) Specifies the urban surface roughness length, meters (optional,

defaults to 1.0m; value other than 1.0m treated as non-DFAULT)
POLLUTID Pollut where: Pollut Identifies type of pollutant being modeled. Any name of up to eight characters may be used, e.g., SO2 , NOX , CO , PM25 , PM-2.5 , PM10 , PM-10 , TSP or OTHER

.
NOTE: Some processing options are pollutant-specific, and require the user to specify the appropriate pollutant ID. For example, use of PM10 , PM-10 , PM25 , PM2.5 , PM-2.5 , PM-25 , LEAD , NO2 , SO2 , or OTHER allows for the use of the MULTYEAR option.

Use of PM25 , PM2.5 , PM-2.5 , or PM-25 , triggers special processing for the PM-2.5 NAAQS, based on values averaged across the number of years processed (see Section 2.1.5.1).

Use of NO2 or SO2 triggers special processing for their respective 1-hr NAAQS based on daily maximum 1-hour concentrations, averaged across the number of years processed, if the CO AVERTIME keyword includes 1-hour averages.

Use of NO2 is required in order to use the OLM and PVMRM options for simulating conversion of NO to NO 2 .
Use of SO2 also triggers the use of a 4-hour half-life for SO 2 decay for urban applications under the regulatory default option.
HALFLIFE Haflif where: Haflif Half life used for exponential decay (s) DCAYCOEF Decay where: Decay Decay coefficient for exponential decay (s -1 ) = 0.693/HAFLIFB-8 Keyword Parameters GASDEPDF React F_Seas2 F_Seas5 (Refpoll)
where: React F_Seas2 F_Seas5 (Refpoll) Value for pollutant reactivity factor ( f

o ) Fraction (F) of maximum green LAI for seasonal category 2 Fraction (F) of maximum green LAI for seasonal category 5 Optional name of reference pollutant
GASDEPVD Uservd where: Uservd User-specified dry depos ition velocity (m/s) for gaseous pollutants
GDLANUSE Sec1 Sec2 ... Sec36
where: Sec1 Sec2

.

. Sec36 Land use category for winds blowing toward sector 1 (10 degrees) Land use category for winds blowing toward sector 2 (20 degrees)

Land use category for winds blowi ng toward sector 36 (360 degrees)
GDSEASON Jan Feb ... Dec
where: Jan

.

.

.

.
Dec Seasonal category for January: 1 = Midsummer/Lush vegetation; 2 = Autumn/Unharvested cropland; 3 = Late autumn after harvest or Winter with no snow; 4 = Winter with continuous snow cover; or 5 = Transitional spring/partial green coverage/short annuals)
Seasonal category for December LOW_WIND SVmin (WSmin) [for LOWWIND1] SVmin (WSmin (FRANmax)) [for LOWWIND2]
where: SVmin WSmin FRANmax Minimum value of sigma-v, within a range of 0.01 to 1.0 m/s Minimum value of wind speed, within a range of 0.01 to 1.0 m/s Maximum value meander factor, within a range of 0.50 to 1.0 inclusive NO2EQUIL NO2Equil where: NO2Equil Equilibrium ratio of NO 2 /NO x for the PVMRM and OLM options; between 0.1 and 1.0, inclusive (default is 0.9)
NO2STACK NO2Ratio
where: NO2Ratio Default in-stack ratio of NO 2 /NO x for PVMRM and OLM options, which may be overridden by NO2RATIO keyword on SO pathway.

NOTE: Beginning with version 11059, AERMOD no longer assumes a default in-stack ratio of 0.1 for the OLM option. OZONEFIL O3FileName (O3Units) (O3Format)B-9 Keyword Parameters
where: O3FileName (O3Units) (O3Format) Filename for hourly ozone data f ile (YR, MN, DY, HR, O3Value) Units of ozone data (PPM, PPB, or UG/M3); default is UG/M3 Fortran format statement to read ozone file; default is FREE-format, i.e., comma or space-delimited data fields (Yr Mn Dy Hr O3Value). The O3Format parameter must include open and close parentheses, the date variables must be read as integers (Fortran I format), and the O3Value must be read as real (Fortran F, E, or D format), e.g., ‘(4I2,F8.3)’. The year may be specified as a 2-digit or 4-digit year, and the data period in the OZONEFIL must match the data period in the meteorological data files. OZONEVAL O3Value (O3Units)
where: O3Value
(O3Units) Background ozone concentration; also used to substitute for missing data in OZONEFIL Units of ozone value (PPM, PPB, or UG/M3); default is UG/M3 O3VALUES O3Flag O3values(i), i=1,n where: O3Flag

O3values Background ozone values flag: ANNUAL for annual; SEASON for seasonal; MONTH for monthly; HROFDY for hour-of-day; WSPEED for wind speed category; SEASHR for season-by-hour; HRDOW for emission rates vary by hour-of-day, and day-of-week [M-F, Sat, Sun]; HRDOW7 for emission rates vary by hour-of-day, and the seven days of the week [M, Tu, W, Th, F, Sat, Sun]; SHRDOW for season by hour-of-day by day-of-week (M-F,Sat,Sun); SHRDOW7 for season by hour-of-day by day-of-week (M,Tu,W,Th,F,Sat,Sun); MHRDOW for month by hour-of-day by day-of-week (M-F,Sat,Sun); MHRDOW7 for month by hour-ofday by day-of-week (M,Tu,W,Th,F,Sat,Sun) Array of background con centrations, for: ANNUAL , n=1; SEASON , n=4; MONTH , n=12; HROFDY , n=24; WSPEED , n=6; SEASHR , n=96; HRDOW , n=72; HRDOW7 , n=168; SHRDOW , n=288; SHRDOW7 , n=672; MHRDOW , n=864; MHRDOW7 , n=2016

NOTE: Background ozone values input through the O3VALUES keyword are assumed to be in units of PPB. OZONUNIT (OzoneUnits) where: (OzoneUnits) Ozone concentration units for O3VALUES, specified as PPB for parts-per-billion, PPM for parts-per-million, or UG/M3 for micrograms/cubic-meter. FLAGPOLE (Flagdf) where: (Flagdf) Default value for height of (flagpole) receptors above local ground, a default value of 0.0 m is used if this optional parameter is omitted
RUNORNOT RUN or NOTB-10 Keyword Parameters
where: RUN NOT Indicates to run full model calculations Indicates to process setup data and report errors, but to not run full model calculations EVENTFIL (Evfile) (Evopt) where: (Evfile)
(Evopt) Identifies the filename to be used to generate a file for input to EVENT model (Default=EVENTFIL.INP) Optional parameter to specify the level of output detail selected for

the EVENT model: either SOCONT or DETAIL (default is DETAIL if this parameter is omitted) SAVEFILE (Savfil) (Dayinc) (Savfl2) where: (Savfil)
(Dayinc) (Savfl2) Specifies name of disk file to be used for storing intermediate results (default = SAVE.FIL); file is overwritten after each dump Number of days between dumps (optional: default is 1) Optional second disk filename to be used on alternate dumps - eliminates risk of system crash during the dump. If blank, file is overwritten each time. INITFILE (Inifil) where: (Inifil) Specifies name of disk file of intermediate results to be used for initializing run (default = SAVE.FIL) MULTYEAR (H6H) Savfil (Inifil) where: (H6H)

Savfil
(Inifil) Optional field formerly used to specify that High-Sixth-High is being calculated for use in PM10 processing; no longer required Specifies name of file to be used for storing results at the end of the

year Optional name of file used for initializing the results arrays from

previous year(s). The Inifil parame ter is not used for the first year in the multi-year run.
DEBUGOPT MODEL (Dbgfil) and/or METEOR (Dbmfil) and/or PVMRM (Dbpvfil) and/or DEPOS
where: MODEL (Dbgfil)

METEOR (Dbmfil)

PVMRM (Dbpvfil)

DEPOS Specifies that MODEL debugging output will be generated Optional filename for the model cal culation debug file (a default filename of ‘MODEL.DBG’ will be used if omitted) Specifies that METEOR ological profile data file will be generated Optional filename for the meteorologi cal profile data file (a default filename of ‘METEOR.DBG’ will be used if omitted) Specifies that PVMRM debugging output will be generated Optional filename for PVMRM debug file (a default filename of ‘PVMRM.DBG’ will be used if omitted) Specifies that DEPOS ition debugging output will be generated, using

default filenames of ‘GDEP.DAT’ for gas deposition and ‘PDEP.DAT’ for particle deposition.

Note: The user can specify any of the applicable debug optionsB-11 Keyword Parameters for a particular model run, and the options can be specified in any order. However, the optional filenames must be specified immediately after the keyword option associated with the filename. Also note that some debugging information is written to the main ‘aermod.out’ file for the MODEL and DEPOS debug options. ERRORFIL (Errfil) where: (Errfil) Specifies name of deta iled error listing file (default = ERRORS.LST)B-12 TABLE B-3
DESCRIPTION OF SOURCE PATHWAY KEYWORDS

SO Keywords Type Keyword Description

STARTING M – N Identifies the start of SOURCE pathway inputs
ELEVUNIT O – N Defines input units for source elevations (defaults to meters), must be first keyword after SO STARTING if used.
LOCATION M – R Identifies coordinates for particular source
SRCPARAM M – R Identifies source parameters for a particular source
BUILDHGT O – R Building height values for each wind sector
BUILDLEN O – R Building projected length values for each wind sector
BUILDWID O – R Building projected width values for each wind sector
XBADJ O – R Along-flow distances from the stack to the center of the upwind face of the projected building
YBADJ O – R Across-flow distances from the stack to the center of the upwind face of the projected building
AREAVERT M – R Specifies location of vertices for an AREAPOLY source type (mandatory if AREAPOLY source is used)
URBANSRC O – R Identifies which sources to model with urban effects
EMISFACT O – R Optional input for variable emission rate factors
EMISUNIT O – N Optional unit conversion factors for emissions, concentrations
CONCUNIT O – N Optional conversion factors for emissions and concentrations
DEPOUNIT O – N Optional conversion factors for emissions and depositions
PARTDIAM O – R Input variables for optional input of particle size (microns)
MASSFRAX O – R Optional input of mass fraction for each particle size category
PARTDENS O – R Optional input of particle density (g/cm 3 ) for each size category METHOD_2 O – R Optional input of parameters for METHOD_2 particle deposition
GASDEPOS O – R Optional input of gas deposition parameters
NO2RATIO O – R Option to specify in-stack NO2/NOx equilibrium ratio for OLM and PVMRM options by source
HOUREMIS O – R Option for specifying hourly emission rates in a separate file
BACKGRND O – R Option to specify temporally varying background concentrations
BACKUNIT O – N Option to specify units for background concentrations
INCLUDED O – R Option to include data from a separate file in the runstreamB-13 SO Keywords Type Keyword Description
OLMGROUP O – R Specifies sources to combine for OLM option to account for merging plumes
PSDGROUP 1 O – R Specifies source groups for PSDCREDIT option with PVMRM
SRCGROUP 1 M – R Identification of source groups
FINISHED M – N Identifies the end of SOURCE pathway inputs

1) The PSDGROUP or SRCGROUP keywords must be the last keyword within the SO pathway before the FINISHED keyword. The SRCGROUP keyword is mandatory, unless the PSDCREDIT option is used, which re quires the PSDGROUP option instead.B-14 TABLE B-4
DESCRIPTION OF SOURCE PA THWAY KEYWORDS AND PARAMETERS

Keyword Parameters

ELEVUNIT METERS or FEET
where: METERS

FEET Specifies input units for source base elevations of meters (default if ELEVUNIT is omitted) Specifies input units for source elevations of feet Note: This keyword applies to source base elevations only. LOCATION SrcID Srctyp Xs Ys (Zs) [for all Srctyp’s except LINE ]

or (FLAT) [for ‘FLAT & ELEV’ option]

or SrcID Srctyp Xs1 Ys1 Xs2 Ys2 (Zs) [for LINE Srctyp]

or (FLAT) [for ‘FLAT & ELEV’ option]
where: SrcID
Srctyp

Xs

Ys

Xs1, Xs2 Ys1, Ys2 (Zs)
(FLAT ) Source identification code (unique alphanumeric string of up to 12 characters) Source type: POINT , POINTCAP , POINTHOR , VOLUME ,

AREA , AREAPOLY , AREACIRC , OPENPIT, LINE x-coord of source location, corner for AREA , AREAPOLY , and OPENPIT , center for AREACIRC (m) y-coord of source location, corner for AREA , AREAPOLY , and OPENPIT , center for AREACIRC (m) x-coords of midpoint for start and end of LINE source (m) y-coords of midpoint for start and end of LINE source (m) Optional z-coord of source loca tion (elevation above mean sea level, defaults to 0.0 if omitted) Optional keyword to indicate non-DFAULT option for identifying sources to model as FLAT terrain SRCPARAM SrcID Ptemis Stkhgt Stktmp Stkvel Stkdia (POINT , POINTCAP , POINTHOR source) Vlemis Relhgt Syinit Szinit (VOLUME source) Aremis Relhgt Xinit (Yinit) (Angle) (Szinit) (AREA source) Aremis Relhgt Nverts (Szinit) (AREAPOLY source) Aremis Relhgt Radius (Nverts) (Szinit) (AREACIRC source) Lnemis Relhgt Width (Szinit) (LINE source) Opemis Relhgt Xinit Yinit Pitvol (Angle) (OPENPIT source)
where: SrcID __Emis
___Hgt Source identification code Source emission rate: in g/s for Ptemis and Vlemis; g/(s-m 2 ) for

Aremis, Lnemis, and Opemis Source physical release height above ground (center of height for

VOLUME , height above base of pit for OPENPIT )B-15 Keyword Parameters Stktmp Stkvel Stkdia Syinit Szinit Xinit Yinit
Angle

Nverts

Radius Width Pitvol Stack gas exit temperature (K) Stack gas exit velocity (m/s) Stack inside diameter (m) Initial lateral dimension of VOLUME source (m) Initial vertical dimension of VOLUME , AREA , LINE source (m) Length of side of AREA source in X-direction (m) Length of side of AREA source in Y-direction (m) (optional

parameter, assumed to be equal to Xinit if omitted) Orientation angle (deg) of AREA or OPENPIT source relative to N

measured positive clockwise, rotated around the source location, (Xs,Ys) (optional parameter, assumed to be 0.0 if omitted) Number of vertices used for AREAPOLY or AREACIRC source (optional for AREACIRC sources) Radius of circular area for AREACIRC source (m) Width of LINE source (m) Volume of OPENPIT source (m 3 ) BUILDHGT SrcID (or SrcRange) Dsbh(i), i=1,36
where: SrcID SrcRange

Dsbh Source identification code Range of sources (inclusive) for wh ich building dime nsions apply, entered as two alphanumeric strings separated by a '-' Array of direction-specific building heights (m) beginning with 10 degree flow vector and incrementing by 10 degrees clockwise BUILDLEN SrcID (or SrcRange) Dsbl(i), i=1,36
where: SrcID SrcRange Dsbl Source identification code Range of sources (inclusive) for which building di mensions apply Array of direction-specific buildi ng lengths (m) beginning with 10 degree flow vector and incrementing by 10 degrees clockwise BUILDWID SrcID (or SrcRange) Dsbw(i), i=1,36
where: SrcID SrcRange Dsbw Source identification code Range of sources (inclusive) for which building di mensions apply Array of direction-specific building widths (m) beginning with 10 degree flow vector and incrementing by 10 degrees clockwise XBADJ SrcID (or SrcRange) Xbadj(i), i=1,36
where: SrcID SrcRange Xbadj(i) Source identification code Range of sources (inclusive) for which XBADJ distances apply Array of direction-specific along-wind distances beginning with 10 degree flow vector and incrementing by 10 degrees clockwise YBADJ SrcID (or SrcRange) Ybadj(i), i=1,36
where: SrcID SrcRange Ybadj(i) Source identification code Range of sources (inclusive) for which YBADJ distances apply Array of direction-specific across-wind distances beginning with 10 degree flow vector and incrementing by 10 degrees clockwiseB-16 Keyword Parameters AREAVERT SrcID Xv(1) Yv(1) Xv (2) Yv(2) ... Xv(i) Yv(i)
where: SrcID Xv(1)

Yv(1)

Xv(i) Yv(i) Source identification code X-coordinate of the first vertex of an AREAPOLY source (must be the same as the value of Xs for that source defined on the SO LOCATION card) Y-coordinate of the first vertex of an AREAPOLY source (must be the same as the value of Ys for that source defined on the SO LOCATION card) X-coordinate for the i th vertex of an AREAPOLY source Y-coordinate for the i th vertex of an AREAPOLY source URBANSRC For multiple urban areas: UrbanID SrcID’s and/or SrcRng’s
For single urban areas: SrcID’s and/or SrcRng’s
where: UrbanID SrcID SrcRange Specifies the alphanumeric urban ID (up to eight characters) Specifies which source(s) will be modeled with urban effects Specifies a range of sources that will be modeled with urban effects
EMISFACT SrcID (or SrcRange) Qflag Qfact(i), i=1,n
where: SrcID SrcRange Qflag

Qfact Source identification code Range of sources (inclusive) for which emission rate factors apply Variable emission rate flag: SEASON for seasonal; MONTH for monthly; HROFDY for hour-of-day; WSPEED for wind speed category; SEASHR for season-by-hour; HRDOW for emission rates vary by hour-ofday, and day-of-week [M-F, Sat, Sun]; HRDOW7 for emission rates vary by hour-of-day, and the seven days of the week [M, Tu, W, Th, F, Sat, Sun]; SHRDOW for season by hour-of-day by day-of-week (M-F,Sat,Sun); SHRDOW7 for season by hour-ofday by day-of-week (M,Tu,W,Th,F,Sat,Sun); MHRDOW for month by hour-of-day by day-of-week (M-F,Sat,Sun); MHRDOW7 for month by hour-of-day by day-of-week (M,Tu,W,Th,F,Sat,Sun) Array of scalar emission rate factors, for: SEASON , n=4; MONTH , n=12; HROFDY , n=24; WSPEED , n=6; SEASHR , n=96; HRDOW , n=72; HRDOW7 , n=168; SHRDOW , n=288; SHRDOW7 , n=672; MHRDOW , n=864; MHRDOW7 , n=2016
EMISUNIT Emifac Emilbl Outlbl
where: Emifac

Emilbl Emission rate factor used to adjust units of output (default value is 1.0E06 for CONC for grams to micrograms; default value is 3600 for grams/sec to grams/m 2 /hr for deposition) Label to use for emission units (default is grams/sec)B-17 Keyword Parameters Outlbl Label to use for output units; applies to first output type if more than one output type is genera ted (default is micrograms/m**3 for concentration and grams/m**2 for deposition)
CONCUNIT Emifac Emilbl Conlbl
where: Emifac

Emilbl Conlbl Emission rate factor used to adjust units of output (default value is 1.0E06 for concentration for grams to micrograms) Label to use for emission units (default is grams/sec) Label to use for concentrations (default is micrograms/m 3 ) DEPOUNIT Emifac Emilbl Deplbl
where: Emifac

Emilbl Deplbl Emission rate factor used to adjust units of output for deposition (default value is 3600 for grams/sec to grams/m 2 /hr) Label to use for emission units (default is grams/sec) Label to use for deposition (default is grams/m 2 ) PARTDIAM SrcID (or SrcRange) Pdiam(i), i=1,Npd
where: SrcID SrcRange Pdiam Source identification code Range of sources (inclusive) for which size categories apply Array of particle diameters (microns) MASSFRAX SrcID (or SrcRange) Phi(i), i=1,Npd
where: SrcID SrcRange Phi Source identification code Range of sources (inclusive) for which mass fractions apply Array of mass fractions for each particle size category PARTDENS SrcID (or SrcRange) Pdens(i), i=1,Npd
where: SrcID SrcRange Pdens Source identification code Range of sources (inclusive) for which particle densities apply Array of particle densities (g/cm 3 ) for each size category METHOD_2 SrcID (or SrcRange) FineMassFraction Dmm
where: SrcID FineMassFraction

Dmm Source identification code Fraction (between 0 and 1) of par ticle mass emitted in fine mode, less than 2.5 microns Representative mass mean particle diameter in microns GASDEPOS SrcID (or SrcRange) Da Dw rcl Henry
where: SrcID Da Dw rcl Henry Source identification code Diffusivity in air for the pollutant being modeled (cm 2 /s) Diffusivity in water for the pollutant being modeled (cm 2 /s) Cuticular resistance to uptake by lipids for individual leaves (s/cm) Henry's Law constant (Pa m 3 /mol) NO2RATIO SrcID (or SrcRange) NO2Ratio
where: SrcID SrcRange Source identification code Source ID range for specified ratioB-18 Keyword Parameters
NO2Ratio In-stack ratio of NO 2 /NO x HOUREMIS Emifil SrcID's SrcRange's
where: Emifil SrcID's SrcRange's Specifies name of the hourly emission rate file Discrete source IDs that are incl uded in the hourly emission file Source ID ranges that are included in the hourly emission file BACKGRND BGflag BGvalue(i), i=1,n and/or HOURLY BGfilnam (BGformat) where: BGflag

BGvalue

HOURLY

BGfilnam (BGformat) Variable background concentration flag: ANNUAL for annual; SEASON for seasonal; MONTH for monthly; HROFDY for hour-of-day; WSPEED for wind speed category; SEASHR for season-by-hour; HRDOW for emission rates vary by hour-of-day, and day-of-week [M-F, Sat, Sun]; HRDOW7 for emission rates vary by hour-of-day, and the seven days of the week [M, Tu, W, Th, F, Sat, Sun]; SHRDOW for season by hour-of-day by day-of-week (M-F,Sat,Sun); SHRDOW7 for season by hour-of-day by day-of-week (M,Tu,W,Th,F,Sat,Sun); MHRDOW for month by hour-of-day by day-of-week (M-F,Sat,Sun); MHRDOW7 for month by hourof-day by day-of-week (M,Tu,W,Th,F,Sat,Sun) Array of background concentrations; for: ANNUAL , n=1; SEASON , n=4; MONTH , n=12; HROFDY , n=24; WSPEED , n=6; SEASHR , n=96; HRDOW , n=72; HRDOW7 , n=168; SHRDOW , n=288; SHRDOW7 , n=672; MHRDOW , n=864; MHRDOW7 , n=2016
Flag indicating that hourly background concentrations are specified

in a separate data file; data period must match the meteorological data period being processed; no missing values are allowed in the hourly file, unless temporally-var ying background concentrations are also specified through the BG flag parameter, which are used to substitute for missing hourly values. Filename for hourly background concentrations Optional Fortran format of hourly background concentration file;

the default format is FREE format, i.e., comma or spacedelimited data fields (Yr Mn Dy Hr BGvalue). The BGformat parameter must include open and close parentheses, the date variables must be read as integers (Fortran I format), and the BGvalue must be read as real (Fortran F, E, or D format), e.g., ‘(4I2,F8.3)’. The year may be specified as a 2-digit or 4-digit year, and the data period in the HOURLY background file must match the data period in the meteorological data files.

NOTE: Background concentrations specified on theB-19 Keyword Parameters BACKGRND keyword are currently assumed to be in units of PPB for NO 2 and SO 2 , PPM for CO, and UG/M3 for all other pollutants, unless otherwise specified on the SO BACKUNIT keyword.
Background concentrations can be included with any source group, including group ‘ALL’, by including a “SrcID” of ‘BACKGROUND’ on the SRCGROUP keyword.
BACKUNIT BGunits where: BGunits Background concentration units, specified as PPB for parts-perbillion, PPM for parts-per-million, or UG/M3 for micrograms/cubic-meter. Background concentrations input in units of PPB or PPM are converted to micrograms/cubic-meter based on reference temperature (25 C) and pressure (1013.25 mb).
INCLUDED Incfil
where: SrcIncFile Filename for the incl uded source file, up to 200 characters in length; double quotes (“) may be used as delimiters for the filename to allow for embedded spaces; and quotes don’t count toward the limit of 200 OLMGROUP OLMGrpID SrcID's SrcRange's where: OLMGrpID SrcID's SrcRange's Group ID (Grpid = ALL specifies group including all sources) Discrete source IDs to be included in group Source ID ranges to be included in group

Note : Card may be repeated with same Grpid if more space is needed to specify sources PSDGROUP PSDGrpID SrcID's SrcRange's where: PSDGrpID

SrcID's SrcRange's PSD GrpID for PSDCREDIT option, must be one of the following: INCRCONS – increment-consuming sources, NONRBASE – non-retired baseline sources, or RETRBASE – retired (increment-expanding) baseline sources. Discrete source IDs to be included in group Source ID ranges to be included in group

Note : Card may be repeated with same PSDGrpID if more space is needed to specify sources SRCGROUP SrcGrpID SrcID's SrcRange's where: SrcGrpID SrcID's Group ID (Grpid = ALL specifies group including all sources) Discrete source IDs to be included in group; a “SrcID” of ‘BACKGROUND’ can be used to include background concentrations, based on the BACKGRND keywordB-20 Keyword Parameters SrcRange's Source ID ranges to be included in group

Note : Card may be repeated with same Grpid if more space is needed to specify sourcesB-21 TABLE B-5
DESCRIPTION OF RECEPTOR PATHWAY KEYWORDS

RE Keywords Type Keyword Description

STARTING M – N Identifies the start of RECEPTOR pathway inputs
ELEVUNIT O – N Defines input units for receptor elevations (defaults to meters), must be first keyword after RE STARTING if used.
GRIDCART O 1 – R Defines a Cartesian grid receptor network
GRIDPOLR O 1 – R Defines a polar receptor network
DISCCART O 1 – R Defines the discretely placed receptor lo cations referenced to a Cartesian system
DISCPOLR O 1 – R Defines the discretely placed receptor lo cations referenced to a polar system
EVALCART O 1 – R Defines discrete Cartesian receptor lo cations for use with EVALFILE output option
INCLUDED O – R Identifies an external file containing r eceptor locations to be included in the inputs
FINISHED M - N Identifies the end of RECEPTOR pathway inputs

1) At least one of the following must be present: GRIDCART, GRIDPOLR, DISCCART, DISCPOLR, or EVALCART, unless the INCLUDED keyword is used to include receptor inputs from an external file. Multiple receptor networks can be specified in a single run, including both Cartesian and polar.B-22 TABLE B-6
DESCRIPTION OF RECEPTOR PATH WAY KEYWORDS AND PARAMETERS

Keyword Parameters

ELEVUNIT METERS or FEET
where: METERS FEET Specifies input units for receptor elevations of meters Specifies input units for receptor elevations of feet Note: This keyword app lies to receptor elevations only.
GRIDCART Netid STA XYINC Xinit Xnum Xdelta Yinit Ynum Ydelta or XPNTS Gridx1 Gridx2 Gridx3 .... GridxN, and YPNTS Gridy1 Gridy2 Gridy3 .... GridyN ELEV Row Zelev1 Zelev2 Zelev3 ... ZelevN HILL Row Zhill1 Zhill2 Zhill3 ... ZhillN FLAG Row Zflag1 Zflag2 Zflag3 ... ZflagN END
where: Netid

STA XYINC Xinit Xnum Xdelta Yinit Ynum Ydelta XPNTS

Gridx1 GridxN YPNTS
Gridy1 GridyN ELEV Row Zelev HILL Row Zhill FLAG Row Zflag

END Receptor network identification c ode (up to eight alphanumeric characters) Indicates STA rt of GRIDCART subpathway, repeat for each new Netid Keyword identifying grid network generated from x and y increments Starting local x-axis grid location in meters Number of x-axis receptors Spacing in meters between x-axis receptors Starting local y-axis grid location in meters Number of y-axis receptors Spacing in meters between y-axis receptors Keyword identifying grid network defined by series of x and y

coordinates Value of first x-coordinate for Cartesian grid Value of 'nth' x-coordinate for Cartesian grid Keyword identifying grid network defined by series of x and y

coordinates Value of first y-coordinate for Cartesian grid Value of 'nth' y-coordinate for Cartesian grid Keyword to specify that receptor elevations follow Indicates which row (y-coordinate fixed) is being input An array of receptor terrain elevations for a particular Row Keyword to specify that hill height scales follow Indicates which row (y-coordinate fixed) is being input An array of hill height scales for a particular Row Keyword to specify that flagpole receptor heights follow Indicates which row (y-coordinate fixed) is being input An array of receptor heights above local terrain elevation for a particular

Row (flagpole receptors) Indicates END of GRIDCART subpathway, repeat for each new NetidB-23 Keyword Parameters
GRIDPOLR Netid STA ORIG Xinit Yinit, or ORIG Srcid DIST Ring1 Ring2 Ring3 ... RingN DDIR Dir1 Dir2 Dir3 ... DirN, or GDIR Dirnum Dirini Dirinc ELEV Dir Zelev1 Zelev2 Zelev3 ... ZelevN HILL Dir Zhill1 Zhill2 Zhill3 ... ZhillN FLAG Dir Zflag1 Zflag2 Zflag3 ... ZflagN END
where: Netid

STA ORIG

Xinit Yinit Srcid DIST Ring1 RingN DDIR Dir1 DirN GDIR Dirnum Dirini Dirinc ELEV Dir Zelev HILL Row Zhill

FLAG Dir Zflag

END Receptor network identification c ode (up to eight alphanumeric characters) Indicates STA rt of GRIDPOLR subpathway, repeat for each new Netid Optional keyword to specify the origin of the polar network (assumed to

be at x=0, y=0 if omitted) local x-coordinate for origin of polar network (m) local y-coordinate for origin of polar network (m) Source ID of source used as origin of polar network Keyword to specify distances for the polar network Distance to the first ring of polar coordinates (m) Distance to the 'nth' ring of polar coordinates (m) Keyword to specify discrete direction radials for the polar network First direction radial in degrees (1 to 360) The 'nth' direction radial in degrees (1 to 360) Keyword to specify generated direction radials for the polar network Number of directions used to define the polar system Starting direction of the polar system Increment (in degrees) for defining directions Keyword to specify that receptor elevations follow Indicates which direction is being input An array of receptor terrain elevations for a particular direction radial Keyword to specify that hill height scales follow Indicates which row (y-coordinate fixed) is being input An array of hill height scales for a par ticular Row Keyword to specify that

flagpole receptor heights follow Keyword to specify that flagpole receptor heights follow Indicates which direction is being input An array of receptor heights above local terrain elevation for a particular

direction (flagpole receptors) Indicates END of GRIDPOLR subpathway, repeat for each new Netid DISCCART Xcoord Ycoord (Zelev Zhill) (Zflag)
where: Xcoord Ycoord (Zelev)
(Zhill) local x-coordinate for discrete receptor location (m) local y-coordinate for discrete receptor location (m) Elevation above sea level for discrete receptor location (optional), used

only for ELEV terrain Hill height scale (optional)B-24 Keyword Parameters (Zflag) Receptor height (flagpole) above lo cal terrain (optional), used only with FLAGPOLE keyword DISCPOLR Srcid Dist Direct (Zelev Zhill) (Zflag)
where: Srcid

Dist Direct (Zelev)
(Zhill) (Zflag) Specifies source identification for whic h discrete polar receptor locations apply (used to define the origin for the discrete polar receptor) Downwind distance to receptor location (m) Direction to receptor location, in degrees clockwise from North Elevation above sea level for receptor location (optional), used only for

ELEV terrain Hill height scale (optional) Receptor height (flagpole) above local terrain (optional), used only with

FLAGPOLE keyword EVALCART Xcoord Ycoord Zelev Zhill Zflag Arcid (Name)
where: Xcoord Ycoord Zelev

Zhill Zflag

Arcid
(Name) Local x-coordinate for discrete receptor location (m) Local y-coordinate for discrete receptor location (m) Elevation above sea level for discrete receptor location (optional), used only for ELEV terrain Hill height scale (m) Receptor height (flagpole) above local terrain (optional), used only with FLAGPOLE keyword Receptor arc ID used to group receptors along an arc or other grouping (up to eight characters) Optional name for receptor (up to eight characters)
INCLUDED RecIncFile
where: RecIncFile Identifies the filename for the included receptor file, up to 200 characters in length; double quotes (“) may be u sed as delimiters for the filename to allow for embedded spaces; quotes don’t count toward the limit of 200B-25 TABLE B-7
DESCRIPTION OF METEORO LOGY PATHWAY KEYWORDS

ME Keywords Type Keyword Description
STARTING M – N Identifies the start of M ETEOROLOGY pathway inputs
SURFFILE M – N Describes input meteorological surface data file
PROFFILE M – N Describes input meteorological profile data file
SURFDATA M – N Describes surface meteorological station
UAIRDATA M – N Describes upper air meteorological station
SITEDATA O – N Describes on-site meteorological station
PROFBASE M – N Specifies the base elevation for the potential temperature profile
STARTEND O – N Specifies start and end dates to be read from input meteorological data file (default is to read entire file)
DAYRANGE O – R Specifies days or ranges of days to process (default is to process all data)
SCIMBYHR O – N Specifies the parameters for the SCIM (Sampled Chronological Input Model) option (see CO MODELOPT)
WDROTATE O – N May be used to correct for alignment problems of wind direction measurements, or to convert wind direction from to flow vector
WINDCATS O – N Input upper bounds of wind speed categories, five values input - sixth category is assumed to have no uppe r bound (used for WSPEED option on the EMISFACT keyword)
FINISHED M – N Identifies the end of METEOROLOGY pathway inputsB-26 TABLE B-8
DESCRIPTION OF METEOROLOGY PA THWAY KEYWORDS AND PARAMETERS

Keyword Parameters
SURFFILE Sfcfil where: Sfcfil Specify filename for surface meteorological input file Note: FREE format is used for all SURFFILE reads beginning with version 09292.
PROFFILE Profil where: Profil Specify filename for profile meteorological input file Note: FREE format is used for all PROFFILE reads beginning with version 09292. SURFDATA Stanum Year (Name) (Xcoord Ycoord)
where: Stanum Year (Name) (Xcoord) (Ycoord) Station number, e.g. 5-digit WBAN number for NWS station Year of data being processed (four digits) Station name (optional) x-coordinate of station location (m) (optional) y-coordinate of station location (m) (optional) UAIRDATA Stanum Year (Name) (Xcoord Ycoord)
where: Stanum Year (Name) (Xcoord) (Ycoord) Station number, e.g. 5-digit WBAN number for NWS station Year of data being processed (four digits) Station name (optional) x-coordinate of station location (m) (optional) y-coordinate of station location (m) (optional) SITEDATA Stanum Year (Name) (Xcoord Ycoord)
where: Stanum Year (Name) (Xcoord) (Ycoord) Station number for on-site me teorological data station Year of data being processed (four digits) Station name (optional) x-coordinate of station location (m) (optional) y-coordinate of station location (m) (optional) PROFBASE BaseElev (Units)
where: BaseElev (Units) Base elevation (above MSL) for the potential temperature profile Units of BaseElev: METERS or FEET (default is METERS ) STARTEND Strtyr Strtmn Strtdy (Strthr) Endyr Endmn Enddy (Endhr) where: Strtyr Strtmn Strtdy (Strthr) Endyr Year of first record to be read Month of first record to be read Day of first record to be read Hour of first record to be read (optional) Year of last record to be readB-27 Keyword Parameters
Endmn Enddy (Endhr) Month of last record to be read Day of last record to be read Hour of last record to be read (optional)

Note: File read begins with hour 1 of the start date and ends with hour 24 of the end date if Stahr and Endhr are omitted. DAYRANGE Range1 Range2 Range3 ... RangeN where: Range1

RangeN First range of days to process, either as individual day (XXX) or as range (XXX-YYY); days may be input as Julian dates (XXX) or as month and day (XX/YY) The 'N-th' range of days to process
NUMYEARS NumYrs where: NumYrs Specifies the number of years of meteorological data being processed for purposes of allocating array storage for the OU MAXDCONT option. A default value of 5 years is assumed if the optional NUMYEARS keyword is omitted. SCIMBYHR NRegStart NRegInt (SfcFilnam PflFilnam) where: NRegStart
NRegInt (SfcFilnam)
(PflFilnam) Specifies the first hour to be sampled with the SCIM option; required to have a value from 1 to 24 Specifies the sampling interval, in hours Optional output file name to list the surface meteorological data for

the sampled hours Optional output file name to list th e profile meteorological data for

the sampled hours WDROTATE Rotang where: Rotang Specifies angle (in degrees) to rotate wind direction measurements to correct for alignment problems; value of Rotang is subtracted from WD measurements, i.e., rotation is counterclockwise
WINDCATS Ws1 Ws2 Ws3 Ws4 Ws5
where: Ws1 Ws2 Ws3 Ws4 Ws5 Upper bound of first wind speed category (m/s) Upper bound of second wind speed category (m/s) Upper bound of third wind speed category (m/s) Upper bound of fourth wind speed category (m/s) Upper bound of fifth wind speed category (m/s) (sixth category is assumed to have no upper bound)B-28 TABLE B-9
DESCRIPTION OF EVENT PATHWAY KEYWORDS

EV Keywords Type Keyword Description
STARTING M – N Identifies the start of EVENT pathway inputs
EVENTPER M – R Describes data and averaging period for an event
EVENTLOC M – R Describes receptor location for an event
INCLUDED O – R Identifies an external file containing EVENT data to be included in the inputs
FINISHED M – N Identifies the end of EVENT pathway inputsB-29 TABLE B-10
DESCRIPTION OF EVENT PATH WAY KEYWORDS AND PARAMETERS

Keyword Parameters EVENTPER Evname Aveper Grpid Date
where: Name
Grpid Aveper Date Specify name of event to be processed (e.g. H002H24ALL), (up to ten alphanumeric characters) Specify source group ID for event Specify averaging period for event Specify data period for event (ending YYMMDDHH for averaging period)
EVENTLOC Evname XR= Xr YR= Yr (Zelev Zhill) (Zflag)

or RNG= Rng DIR= Dir (Zelev Zhill) (Zflag)
where: Evname

XR= YR= RNG= DIR= (Zelev) (Zhill) (Zflag) Specify name of event to be processed (e.g. H002H24ALL), (up to ten alphanumeric characters) X-coordinate for event (discrete Cartesian receptor) Y-coordinate for event (discrete Cartesian receptor) Distance range for event (discrete polar receptor) Radial direction for event (discrete polar receptor) Terrain elevation for event (optional) Hill height scale (optional) Receptor height above ground for event (optional)
INCLUDED EventIncFile where: EventIncFile Identifies the filename for the included EVENT file, up to 200 characters in length; double quotes (“) may be used as delimiters for the filename to allow for embedded spaces; and quotes don’t count toward the limit of 200

Note: EVENT locations can be input as either discrete Cartesian receptors (XR= , YR= ) or as discrete polar receptors (RNG= , DIR= ). Events that are specified in the file generated by the AERMOD model (CO EVENTFIL card) are always given as discrete Cartesian coordinates. Discrete polar receptors are assumed to be relative to an origin of (0,0).B-30 TABLE B-11
DESCRIPTION OF OUTPUT PATHWAY KEYWORDS

OU Keywords Type Keyword Description

STARTING M – N Identifies the start of OUTPUT pathway inputs
RECTABLE O – R Option to specify value(s) by receptor for output
MAXTABLE O – R Option to summarize the overall maximum values
DAYTABLE O – N Option to print summaries for each averaging period for each day processed.
MAXIFILE O – R Option to list events exceeding a threshold value to file (if CO EVENTFIL option is used, these events are included in the input file generated for the EVENT model).
POSTFILE 1 O – R Option to write results to a mass storage file for postprocessing.
PLOTFILE 1 O – R Option to write certain results to a storage file suitable for input to plotting routines
TOXXFILE O – R Option to write results to a storag e file suitable for input to the TOXX model component of TOXST or the RISK
RANKFILE O – R Option to output file of ranked values for Q-Q plots (must be used with the MAXTABLE keyword)
EVALFILE O – R Option to output file of normalized arc maxima from EVALCART receptors for model evaluation studies
SEASONHR O – R Option to output results by season and hour-of-day
MAXDAILY O – R Option to output file of daily maximum 1-hour values for each day processed; only applicable for 1-hour NO 2 and 1-hour SO 2 NAAQS

MXDYBYYR O – R Option to output file of daily maximum 1-hour values by year, for each year processed; only applicable for 1-hour NO 2 and 1-hour SO 2 NAAQS
MAXDCONT O – R Option to output contri butions of each source group to ranked values averaged across years for a reference source group, paired in time and space; only applicable for 24-hour PM2.5, 1-hour NO 2 , and 1-hour SO 2 NAAQS
SUMMFILE O – N Option to output summary of high ranked values to separate file
FILEFORM O – N Specify fixed or exponential format for output results files
NOHEADER O – N Option to suppress file headers for output file options, e.g., POSTFILE, PLOTFILE, MAXDCONT, etc.
EVENTOUT M – N Specifies the level of output information provided for EVENT Processing [EVENT Only]
FINISHED M – N Identifies the end of OUTPUT pathway inputsB-31 1) POSTFILE is used to output concurrent concentration values for particular source groups and averaging times across the receptor network suitable for postprocessing. PLOTFILE is used to output specific design values, such as second high concentrations, across the receptor network, suitable for plotting concentration contours.B-32 TABLE B-12
DESCRIPTION OF OUTPUT PA THWAY KEYWORDS AND PARAMETERS

Keyword Parameters RECTABLE Aveper FIRST SECOND . . . SIXTH . . . TENTH and/or Aveper 1ST 2ND . . . 6TH . . . 10TH and/or Aveper 1 2 . . . 6 . . . 10

. . . N . . . 999 where: Aveper

FIRST SECOND SIXTH 1ST 2ND 6TH N Averaging period to summarize with high values (keyword ALLAVE specifies all short-term averaging periods) Select summaries of FIRST highest values by receptor Select summaries of SECOND highest values by receptor Select summaries of SIXTH highest values by receptor Select summaries of 1ST highest values by receptor Select summaries of 2ND highest values by receptor Select summaries of 6TH highest values by receptor Select summaries of N -th highest values by receptor (up to 999 -th highest values)

Note: If two parameters are input separated by a dash (e.g. FIRST-THIRD or 4-12 ), then summaries of all high ranked values within that range (inclusive) are provided.
If the CO EVENTFIL keyword is exercised, then the events generated by the RECTABLE keyword are included in the input file for EVENT model.
The range of ranks specified on the RECTABLE keyword (but not the individual ranks specified) also determines the range of ranks that may be considered with the MAXDCONT option. MAXTABLE Aveper Maxnum where: Aveper

Maxnum Averaging period to summarize with overall maximum values (keyword ALLAVE specifies all averaging periods) Specifies number of overall maximum values to summarize DAYTABLE Avper1 Avper2 Avper3 . . . where: Avper1 Averaging period, e.g., 24 for 24-hr averages, to summarize with values by receptor for each day of data processed (keyword ALLAVE for first parameter specifies all averaging periods) MAXIFILE Aveper GrpID Thresh Filnam (Funit) where: Aveper Specifies averaging period for list of values equal to or exceeding a threshold valueB-33 Keyword Parameters GrpID Thresh Filnam Funit Specifies source group to be output to file Threshold value (e.g. NAAQS) for list of exceedances Name of disk file to store maximum values Optional parameter to specify the file unit

Note: If the CO EVENTFIL keyword is exercised, then the events generated by the MAXIFILE keyword are included in the input file for EVENT processing. POSTFILE Aveper GrpID Format Filnam (Funit) where: Aveper
GrpID Format

Filnam Funit Specifies averaging period to be output to file, e.g., 24 for 24-hr averages, PERIOD for period averages Specifies source group to be output to file Specifies format of file, either UNFORM for unformatted files or PLOT for formatted files for plotting Specifies filename for output file Optional parameter to specify the file unit PLOTFILE Aveper GrpID Hivalu Filnam (Funit) (Short Term values) Aveper GrpID Filnam (Funit) (PERIOD or ANNUAL averages) where: Aveper
GrpID Hivalu

Filnam Funit Specifies averaging period to be output to file, e.g., 24 for 24-hr averages, PERIOD for period averages, etc. Specifies source group to be output to file Specifies rank to be included in high value summary (e.g. FIRST , SECOND , 1ST , 2ND , etc.) to be output to file (the rank must be included on the RECTABLE card) Specifies filename for output file Optional parameter to specify the file unit TOXXFILE Aveper Cutoff Filnam (Funit) where: Aveper

Cutoff

Filnam Funit Specifies averaging period to be output to file, e.g., 1 for 1-hr averages. Specifies cutoff (threshold) value in g/m 3 for outputting results for AERMOD model Specifies filename for output file Optional parameter to specify the file unit RANKFILE Aveper Hinum Filnam (Funit) where: Aveper

Hinum Filnam Funit Specifies averaging period to be output to file, e.g., 24 for 24-hr averages Specifies the number of high values to be ranked Specifies filename for output file Optional parameter to specify the file unit EVALFILE SrcID Filnam (Funit) where: SrcID Specifies the source ID to be output to fileB-34 Keyword Parameters
Filnam Funit Specifies filename for output file Optional parameter to specify the file unit SEASONHR GrpID FileName (FileUnit) where: GrpID FileName (FileUnit) Specifies the source group ID to be output to file Specifies filename for output file Optional parameter to specify file unit MAXDAILY GrpID FileName (FileUnit) where: GrpID FileName (FileUnit) Specifies the source group ID to be output to file Specifies filename for output file Optional parameter to specify file unit MXDYBYYR GrpID FileName (FileUnit) where: GrpID FileName (FileUnit) Specifies the source group ID to be output to file Specifies filename for output file Optional parameter to specify file unit MAXDCONT GrpID UpperRank LowerRank FileName (FileUnit)

or GrpID UpperRank THRESH ThreshValue FileName (FileUnit) where: GrpID UpperRank LowerRank

THRESH

ThreshValue

FileName (FileUnit) Specifies the source group ID to be output to file Upper bound of ranks to evaluate for contributions Lower bound of ranks to evaluate for contributions (note that lower rank refers to lower concentra tions and higher rank refers to higher concentrations) NOTE: The UpperRank and LowerR ank values must be within the range of ranks specified on the RECTABLE keyword. AERMOD will analyze each rank w ithin the range, regardless of whether the rank is specified explicitly on the RECTABLE keyword. Indicates that a threshold concentration (ThreshValue) will be specified as a limit on the lower bound rank to process Lower threshold value for evalua ting contributions; processing will stop after the first ranked value that is below ThreshValue NOTE: The ThreshValue analysis will be limited to the range of ranks specified on the RECTABLE keyword (but not the individual ranks that are specified). A warning message is generated if the ThreshValue is not reached within the range of ranks analyzed. Specifies filename for output file Optional parameter to specify file unit

Note:

The range of ranks specified on the RECTABLE keyword (but not the individual ranks specified) also determinesB-35 Keyword Parameters the range of ranks that may be considered with the MAXDCONT option, even with the THRESH option.
SUMMFILE SummFileName where: SummFileName Specifies filename of output summary file
FILEFORM EXP or FIX
where: EXP

FIX Specifies that the output results files will use EXPonentialformatted values Specifies that the output results files will use FIXed-formatted values (fixed-formatted values will be used if FILEFORM is omitted) NOHEADER FileType1 FileType2 FileType3 . . . FileType N

or ALL where: FileType N

ALL Specifies the output file type(s) for which header records will be suppressed; includes the following file types: POSTFILE, PLOTFILE, MAXIFILE, RANKFILE, SEASONHR, MAXDAILY, MXDYBYYR, and MAXDCONT Specifies that header record s will be suppressed for ALL applicable output file types
EVENTOUT SOCONT or DETAIL [EVENT Only]
where: SOCONT DETAIL Provide source contribution information only in the event output Include hourly concentrations for each source and hourly meteorological data in the event outputC-1 

### APPENDIX C. LIST OF ERROR/WARNING MESSAGES

This appendix provides a list of error, warning and inform ational messages used in the
current version of the AERMOD model. Three t ypes of messages can be produced by the model during processing of model inputs and during mo del calculations. These are described below:

• Fatal Errors that will halt any further processin g, except to identify additional error conditions (type E);

• Warnings that do not halt processing but i ndicate possible errors or suspect conditions (type W); and

• Informational messages that may be of interest to the user but have no direct bearing on the validity of the results (type I).

A more detailed explanation of the error handling and reporting procedures used in AERMOD is provided in Appendix C of the AERMOD User’s Guide (EPA, 2004a). The three message types are identified with the letters E (errors), W (warnings), and I (informational messages). The 3-digit message numbers are generally grouped in to categories corresponding to the different stages of the processing, although these distin ctions may not always be obvious. These categories are:

100 - 199 Input Runstream Image Structure Processing 200 - 299 Parameter Setup Processing 300 - 399 Data and Quality Assurance Processing 400 - 499 Run Time Message Processing 500 - 599 Input/Output Message Processing

The list provided below includes the message nu mber, the main message text, and the “hint” field that may include additional details regarding the message. Note that the listing of messages in the AERMOD User’s Guide (EPA, 2004a) is not up-to-date. Several additional messages have been added to AERMOD sin ce that time, and the numbering of some messages may have changed.C-2 Message Number Error/Warning Message Hint
100 Invalid Pathway Specified. The Troubled Pathway is Path 105 Invalid Keyword Specified. The Troubled Keyword is Keyword
109 Too many fields specified on runstream image; MAX=
110 Keyword is Not Valid for This Pathway. Keyword is Path 115 STARTING or FINISHED Out of Sequence: Pathway = Path 120 Pathway is Out of Sequence: Pathway = Path
125 Missing FINISHED-Runstream File Incomplete: ISTAT=
130 Missing Mandatory Keyword. The Missing Keyword is Keyword 135 Nonrepeatable Keyword or Recursed INCLUDED: Keywrd Keyword 140 Invalid Order of Keyword. The Troubled Keyword is Keyword
141 Conflicting Options: PVMRM and OLM both specified
142 Following Keyword Invalid Without PVMRM or OLM: Keyword 143 Following Keyword Invalid Without PVMRM Option: Keyword
144 Following Keyword Invalid Without OLM Option: Keyword 145 Conflicting Options: MULTYEAR and Re-Start Option Keyword 146 PSDGROUP Keyword Specified without PSDCREDIT Opt. Keyword 147 Following Option is Invalid with PSDCREDIT Option: Option
148 O3VALUES keyword will be used instead of OZONEVAL
149 Conflicting options specified on MODELOPT keyword: Option 150 Conflicting Options: MULTYEAR for Wrong Pollutant Keyword
151 Non-DFAULT NoUrbTran option selected on MODELOPT
152 ELEVUNIT card must be first for this Pathway: Path 153 Conflicting Opts: MAXDCONT with Re-Start or MULTYR Keyword 154 Conflicting options: SCIM cannot be used with ST AVEs 155 Conflicting Decay Keyword. Inputs Ignored for Keyword 156 Option ignored - not valid with SCIM. Option = DEPOS 157 Wet SCIM Not Supported - Wet SCIM Inputs Ignored Keyword
158 EMISUNIT Keyword Used With More Than 1 Output Type
159 EMISUNIT Keyword Used With the Following Keyword: Keyword 160 Duplicate ORIG Secondary Keyword for GRIDPOLR: NETID 161 MAXDCONT option already defined for source group: GRPID
162 Option only applies to 1-hr NO2 or 1-hr SO2 NAAQS:
163 Option only applies to 24h PM25, 1h NO2 or 1h SO2:C-3 Message Number Error/Warning Message Hint
164 NOHEADER selected for non-specified output option:
165 Inconsistent temporally-varying BACKGRND options:
166 HOURLY BACKGRND option specified more than once on
170 Invalid Secondary Keyword for Receptor Grid: NETID 175 Missing Secondary Keyword END for Receptor Grid: NETID 180 Conflicting Secondary Keyword for Receptor Grid: NETID
185 Missing Receptor Keywords. No Receptors Specified.
189 No Keywords for OU Path and No PERIOD/ANNUAL Aves.
190 Incompatible Option Used With SAVEFILE or INITFILE Keyword 191 PM-2.5 without MAXIFILE is incompatible with EVENTFIL
192 FASTALL option also implies use of FASTAREA option

193 Units keyword specified without appropriate option CO O3VALUES or SO BACKGRND
194 Option specified on DEBUGOPT keyword not applicable
195 Incompatible Keyword used with GASDEPVD option Keyword 196 Gas deposition algorithms are non-DFAULT options Keyword
197 METHOD_2 for particulates is a non-DFAULT option
198 TOXICS Option obsolete; see Users Guide Addendum
199 Non-DFAULT BETA Option Required for Option
200 Missing Parameter(s). No Options Specified For Keyword 201 Not Enough Parameters Specified For the Keyword of Keyword 202 Too Many Parameters Specified For the Keyword of Keyword 203 Invalid Parameter Specif ied. Troubled Parameter: Parameter 204 Regulatory DFAULT Conflicts with Non-DFAULT Option Option
205 No Option Parameter Setting. Forced by Default to
206 Regulatory DFAULT Overrides Non-DFAULT Option For Option 207 No Parameters Specified. Default Values Will Used. Keyword
208 Illegal Numerical Field Encountered in
209 Negative Value Appears For Non-negative Variable. Variable
210 Number of Short Term Averages Exceeds Max: NAVE =
211 Duplicate Averaging Period Specified for Keyword Keyword
212 END Encountered Without (X,Y) Points Properly Set NETID 213 ELEV Input Inconsistent With Option: Input Ignored NETID 214 ELEV Input Inconsistent With Option: Defaults Used NETIDC-4 Message Number Error/Warning Message Hint 215 FLAG Input Inconsistent With Option: Input Ignored NETID 216 FLAG Input Inconsistent With Option: Defaults Used NETID 217 More Than One Delimiter In A Field for Keyword Keyword
218 Number of (X,Y) Points Not Match With Number Of
219 Number Of Receptors Specified Exceeds Max: NREC =
220 Missing Origin (Use Default = 0,0) In GRIDPOLR NETID 221 Missing Distance Setting In Polar Network NETID 222 Missing Degree Or Dist Setting In Polar Network NETID
223 Missing Distance or Degree Field in
224 Number of Receptor Networks Exceeds Max: NNET =
225 Number of X-Coords Specified Exceeds Max: IXM =
226 Number of Y-Coords Specified Exceeds Max: IYM =
227 No Receptors Were Defined on the RE Pathway.
228 Default(s) Used for Missing Parameters on Keyword Keyword 229 Too Many Parameters - Inputs Ignored on Keyword Keyword 230 Source ID field is too long (>12); first 12 chars: SRCID(1:12) 231 Too Many Numerical Values Specified for EMISFACT
232 Number Of Specified Sources Exceeds Maximum: NSRC=
233 Building Dimensions Specified for Non-POINT Source SRCID 234 Too Many Sectors Input for Keyword
235 Number of Source Groups Exceeds Maximum: NGRP =
236 Not Enough BUILDHGTs Specified for SourceID SRCID 237 Not Enough BUILDWIDs Specified for SourceID SRCID
238 Not Enough BACKGRND Concentration Values Specified
239 Not Enough QFACTs Specified for SourceID SRCID 240 Inconsistent Number of Particle Categories for SRCID
241 Not Enough BUILDLENs Specified for SourceID SRCID 242 No Particle Cat. or Gas Depos. Specified for SRCID SRCID 243 Wet depos (DEPOS, WDEP, WETDPLT) incompatible with GASDEPVD

244 Source parameters are missing or incomplete for DRYDEP or WETDEP
245 No. of Particle Categories Exceeds Max: NPDMAX =
246 Not Enough XBADJs Specified for SourceID SRCID 247 Not Enough YBADJs Specified for SourceID SRCIDC-5 Message Number Error/Warning Message Hint
248 No Sources Were Defined on the SO Pathway.
249 Source elevation is missing (-9999.0); SRCID = SRCID 250 Duplicate XPNT/DIST or YPNT/DIR Specified for GRID NETID 252 Duplicate Receptor Network ID Specified. NETID = NETID
254 Number of Receptor ARCs Exceeds Max: NARC =
256 EVALFILE Option Used Without EVALCART Receptors NUMARC=0 259 Receptor elevation is missing (-9999.0); IREC = Rec Number
260 Number of Emission Factors Exceeds Max: NQF =
261 Not Enough O3VALUES Ozone Concentrations Specified
262 First Vertex Does Not Match LOCATION for AREAPOLY SRCID 264 Too Many Vertices Specified for AREAPOLY Source SRCID 265 Not Enough Vertices Specified for AREAPOLY Source SRCID 266 Invalid shape defined (area=0) for AREAPOLY source SRCID
270 Number of High Values Specified Exceeds Max: NVAL=
272 Upper bound rank > Lower bound rank for MAXDCONT:
273 Range of ranks for MAXDCONT THRESH Opt is limited: Max RANK
275 Number of Max Values Specified Exceeds Max: NMAX=
279 Multiple URBANOPT/URBANSRC inputs not allowed for: URBANSRC ALL
280 Number of Output Types Specified Exceeds Max:NTYP=
281 Number of OLMGROUPs Specified Exceeds Max: NOLM =
282 Following SRCID Included in Multiple OLMGROUPs: SRCID 283 Either OZONEVAL or OZONEFIL Card Needed for Option OLM or PVMRM 284 Invalid POLLUTID Specified for PVMRM/OLM; Must Use NO2
285 Number of Urban Areas Exceeds Maximum. NURB =
286 Following SRCID Included in Multiple PSDGROUPs: SRCID
287 PSDGROUP ID Must be INCRCONS, RETRBASE or NONRBASE
288 Use of "*" for repeated values not meaningful for Keyword 289 Source defined as both particulate and gaseous SRCID
290 Number of Events Specified Exceeds Max: NEVE =
291 Filename specified is too long. Maximum length = ILEN_FLD

292 Potential problem with Fortran format specifier: LEN= ; or NumInts, NumReal 293 User-specified met data format not used; use FREE Format 294 PERIOD and ANNUAL averages are both selected for KeywordC-6 Message Number Error/Warning Message Hint 295 Invalid Averaging Period Specified for SCREEN Mode 1hr Only
296 Averaging Period .NE. 1-Hr for TOXXFILE Option
297 Aver. Period must be .LE. 24 for EVENT Processing EVNAME 298 Error Allocating Storage for Setup Arrays! Error Code 299 Error Allocating Storage for Result Arrays! Error Code
300 Specified SRCID Has Not Been Defined Yet: KEYWORD= Keyword 301 Urban Area ID Has Not Been Defined. URBID = Urban ID 302 Following SRCID Included in Multiple Urban Areas: SRCID 303 Urban ID has already been defined. URBID = Urban ID
305 Stack height > or = EPA formula height for SRCID:
310 Attempt to Define Dup licate LOCATION Card for SRC: SRCID 313 Attempt to Define Duplicate EVENTPER card for EVNAME 315 Attempt to Define Duplicate SRCPARAM Card for SRC: SRCID 317 Specified SRCID not included in any PSD/SRCGROUP: SRCID 318 No Sources Defined for Urban Area. URBID = Urban ID 319 No Sources Included in Specified Source Group: GRPID 320 Input Parameter May Be Out-of-Range for Parameter Parameter 322 Release Height Exceeds Effective Depth for OPENPIT SRCID 324 Release Height Exceeds 3000 Meters for SRCID: SRCID 325 Negative Exit Velocity (Set=1.0E-5) for SRCID: SRCID 330 Mass Fraction Parameters Do Not Sum to 1. for Src SRCID 332 Mass Fraction Parameter Out-of-Range for Source SRCID 334 Particle Density Out-of-Range for Source SRCID 335 Particle Diameter Out-of-Range for Source SRCID 336 NO2RATIO Invalid or Not Specified for PVMRM Source SRCID 338 Neg Emis Rate Cannot be Used with OLM/PVMRM. Src: SRCID 340 Possible Error in PROFBASE Input: Value is < 0 Keyword 342 Src ID Mismatch in Hourly Emissions File for ID = SRCID 344 Missing HOUREMIS fields; EmisRate set = 0. KURDAT= YYMMDDHH 345 Problem processing the HOUREMIS file. KURDAT = YYMMDDHH 346 Too many fields for HOUREMIS file. KURDAT = YYMMDDHH 350 Julian Day Out Of Range at JDAY 352 Missing Field on MULTYEAR Keyword for H6H 353 Urban Roughness Length (m) May Be Out-of-Range: URBZ0C-7 Message Number Error/Warning Message Hint 360 2-Digit Year Specified: Valid for Range 1950-2049 Keyword 361 Multiyear PERIOD/ANNUAL values for NO2/SO2 require MULTYEAR Opt
362 Multiyear 1h NO2/SO2 processing not applicable for option
363 Multiyr 24h/Ann PM25 processing not applicable for option 365 Year Input is Greater Than 2147 Keyword or YR = 370 Invalid Date: 2/29 In a Non-leap Year. YR =
380 This Input Variable is Out-of-Range:
381 Latitude in Surface File Is Not Valid: Lat 382 Error Decoding Latitude: Lat 384 Not enough fields specified for HOUREMIS; KURDAT = YYMMDDHH 386 PARTDIAM and METHOD_2 specified for same SRCID: SRCID 387 METHOD_2 option already specified for this SRCID: SRCID 391 Aspect ratio (L/W) of area source greater than 100 SRCID 392 Aspect ratio (L/W) of open pit is greater than 10 SRCID 395 Met. Data Error; Incompatible Version of AERMET: Version Date 397 SCREEN option used without use of SCREEN Met Data Version Date
398 SCREEN met used without specifying SCREEN option
399 EXP format specified with no applicable file types FILEFORM
400 Output values exceed format limit; use OU FILEFORM = EXP 405 Value of PHEE Exceeds 1.0 on KURDAT = YYMMDDHH 406 Number of Vertices Exceeds Max (NVMAX) for SRCID:: SRCID 410 Wind Direction Out-of-Range. KURDAT = YYMMDDHH
413 Number of Threshold Events > 9999 for Ave Period
415 MAXDCONT THRESH not reached within range of ranks
420 Wind Speed Out-of-Range. KURDAT = YYMMDDHH 430 Ambient Temperature Data Out-of-Range. KURDAT = YYMMDDHH 432 Friction Velocity Out-of-Range. KURDAT = YYMMDDHH 435 Surface Roughness Length Out-of-Range. KURDAT = YYMMDDHH 438 Convective Velocity Data Out-of-Range. KURDAT = YYMMDDHH 439 Monin-Obukhov Length Out-of-Range. KURDAT = YYMMDDHH 440 Calm Hour Identified in Meteorology Data File at YYMMDDHH 441 Vert Pot Temp Grad abv ZI set to min .005, KURDAT= YYMMDDHH 442 Vert Pot Temp Grad abv ZI exceeds 0.1 K/m, KURDAT= YYMMDDHH 450 Record Out of Sequence in Meteorological File at: YYMMDDHHC-8 Message Number Error/Warning Message Hint 452 Missing value in hourly BACKGRND file at KURDAT = YYMMDDHH 453 Substitution for missing hourly BACKGRND data. Date= YYMMDDHH 454 Date/time Mismatch: Hourly BACKGRND file; KURDAT = YYMMDDHH 455 Date/time Mismatch: Hourly Emission File. KURDAT = YYMMDDHH 456 Date/time Mismatch on Surface & Profile. KURDAT = YYMMDDHH 457 Date/time Mismatch on OZONEFIL Data. KURDAT = YYMMDDHH 458 Substitution made for mi ssing ozone data. KURDAT = YYMMDDHH 459 Missing ozone data; Full conversion used. KURDAT = YYMMDDHH 460 Missing Hour Identified in Meteor. Data File at YYMMDDHH
465 Number of Profile Levels Exceeds Max: MXPLVL =
470 Mixing Height Value is < or = 0.0. KURDAT = YYMMDDHH 474 WS RefHt invalid (<0.001); Not msg or clm: KURDAT= YYMMDDHH 475 WS reference height is higher than 100m. KURDAT = YYMMDDHH
480 Less than 1yr for MULTYEAR, MAXDCONT or ANNUAL Ave
481 Data Remaining After End of Year. Number of Hours=
482 Too many years modeled for 24h-PM25 1h-NO2 1h-SO2:
483 User Start Date is Earlier Than Start of Met File YYMMDDHH

484 Restart Date < STARTEND date or start of met file STARTEND or YYMMDDHH

485 MULTYR DataGap; Restart Date < STARTEND or MetFile STARTEND or YYMMDDHH 486 MULTYR Date Overlap; STARTEND Date < Restart Date YYMMDDHH 487 MULTYR Date Overlap; Met File Start < Restart Date YYMMDDHH 488 First met HR.ne.1; ST results may not be valid for First Day 489 First met HR.ne.1; EV results may not be valid for MnDyHr 490 Problem reading SURFFILE date for EVENTS; MNDYHR = MnDyHr
491 MAXDCONT option requires 1st Hr of met data = 01;

495 Surface met file does not include enough variables with-DEP or Non-DEP 496 Total precipitation in SURFFILE is zero (0.0) with WetDepos 498 Possible code ERROR!!! MAXDCONT mismatch for GRPID GRPID 499 PRIME plume rise error; check stack parameters for SRCID

500 Fatal Error Occurs Opening the Data File of FileName or FileType 510 Fatal Error Occurs During Reading of the File of FileTypeC-9 Message Number Error/Warning Message Hint 520 Fatal Error Occurs During Writing to the File of FileType and Unit 530 CAUTION! Met Station ID Mismatch with SURFFILE for Keyword 540 No RECTABLE/MAXTABLE/DAYTABLE for Average Period nnn-HR 550 File Unit/Name Conflict for the Output Option: Keyword

555 File Unit/Name conflict across options: GRP# AVE GrpNum and AvePer 560 User Specified File Unit .LT. 30 for OU Keyword: Keyword 565 Possible Conflict With Dynamically Allocated FUNIT Keyword 570 Problem Reading Temporary Event File for Event: EVNAME 580 End of File Reached Trying to Read the File of Keyword 585 Output data file for INITFILE option was not found File Type
590 The INITFILE filename matches a SAVEFILE filename
592 MAXIFILE includes data past start of MULTYEAR run YYMMDDHH 593 POSTFILE includes data past start of MULTYEAR run YYMMDDHH New messages introduced with version 12345 of AERMOD:
111 LOW_WIND Keyword specified without LOWWIND Options
112 User-specified minimum Sigma-V on LOW_WIND Keyword SVmin 113 User-specified minimum WindSpeed on LOW_WIND Keywd WSmin
114 User-specified maximum FRAN on the LOW_WIND Keywrd FRANmax 116 Vector Wind Speeds specified on MODELOPT Keyword
121 LowWind1 Beta Option specified on MODELOPT Keyword
122 LowWind2 Beta Option specified on MODELOPT Keyword
131 Minimum sigmav value (SVmin) for LowWind1 Beta Opt SVmin 132 Minimum sigmav value (SVmin) for LowWind2 Beta Opt SVmin 133 Maximum FRAN value (FRANmax) for LowWind2 Beta Opt FRANmax 136 Conflicting Beta Option - LowWind1 and LowWind2
186 THRESH_1MIN 1-min ASOS wind speed threshold used Thresh 187 ADJ_U* Beta Option for Low Winds used in AERMET
188 Non-Default ADJ_U* Option used in AERMET without BETA option 341 Emissions in HOUREMIS file < -90; set to 0.0 for YYMMDDHH 492 SURFDATA YR .NE. 1st YR of file, adj to match file
493 SURFDATA YR must match 1st YR of file for DAYRANGE KeywordD-1 

### APPENDIX D

EPA MODEL CLEARINGHOUSE MEMORANDUM DATED JULY 9, 1993D-2 July 9, 1993

MEMORANDUM

SUBJECT: Proposal for Calculating Plume Rise for Stacks with Horizontal Releases or Rain Caps for Cookson Pigment, Newark, New Jersey

FROM: Joseph A. Tikvart, Chief Source Receptor Analysis Branch, TSD (MD-14)

TO: Ken Eng, Chief Air Compliance Branch, Region II

In response to your request, the Model Clearinghouse has reviewed your proposal for treating horizontal and capped stacks at Cookson Pigment so that the model (SCREEN or ISC2) will properly treat plume rise from the Cookson Pigment stacks. We concur in principle with the approach, with some relatively minor changes.

First, the analysis provided by New Jersey Department of Environmental Protection is technically correct. We suggest, however, that the exit velocity for horizontal and capped stacks be set to a lower figure than 0.1 m/s. A 0.1 m/s exit velocity may still result in significant momentum plume rise being calculated, even though these kinds of sources should have zero momentum rise. We therefore suggest setting the stack exit velocity to a lower value, such as .001.

For horizontal stacks that are not capped, we suggest turning stack tip downwash off, whether there are buildings or not. Stack tip downwash calculations are inappropriate for horizontal stacks.

For vertical stacks that are capped, turn stack tip downwash off and reduce the stack height by three times the actual stack diameter. The cap will probably force stack tip downwash most of the time. The maximum amount of the stack tip downwash (as calculated in ISC2) is three times the stack diameter. Reducing the stack height by this amount, while turning off the stack tip downwash option, causes the maximum stack tip downwash effect. The resulting concentrations may err slightly on the high side. For stacks with small diameters, such as those at Cookson Pigment, the error should be quite small. Note, however, that this approach may not be valid for large diameter stacks (say, several meters).

cc: A. Colecchia D. WilsonF-1 

### APPENDIX E. EVALUATION OF MODIFIED URBAN OPTION

The urban option in AERMOD was modified, beginning with version 11059, to address potential issues associated with the transiti on from the nighttime urban boundary layer to the daytime convective boundary layer. Prior to version 11059, the enhanced dispersion associated with the urban nighttime heat island effect was ignored once the boundary layer turned
convective. This could result in an unrealis tic drop in the mixed layer height during early morning hours for urban applications, which co uld contribute to un realistically high concentrations for low-level plumes. This e ffect was observed in the application of AERMOD for the Risk and Exposure Assessm ent (REA) in support of the NO 2 NAAQS review in association with mobile source emissions (EPA , 2008). Beginning with version 11059 the urban option in AERMOD continues application of th e urban boundary layer approach for urban sources until the daytime convective mixing he ight exceeds the urban nighttime mixing height, based on the user-specifi ed population (Cimorelli, et al. , 2004). This revision to AERMOD will generally reduce concentrations during the early morning transiti on to convective conditions for low-level urban sources, but may increase daytime c oncentrations for elevated urban sources.

The modified implementation of the urban opt ion was evaluated using data from the 1985 Indianapolis SF 6 urban field study (Perry, et al, 2005), a nd model-to-monitor comparisons at four
ambient monitors for 2002 from the Atlanta NO 2 REA (EPA, 2008). The Indianapolis study involved an elevated buoyant release and the Atlanta REA st udy involved mostly low-level
mobile source emissions. Results from the Indian apolis study are presented in the form of Q-Q plots of ranked 1-hour modeled vs. observed con centrations, unpaired in time and space. Figure E-1 shows model performance fo r all stabilities and Figure E- 2 shows model performance for convective conditions only. The revised urba n option does not affect results under stable
conditions. Results from the Atlanta NO 2 REA are also presented in the form of Q-Q plots of
1-hour ranked modeled vs. observed concentrati ons, unpaired in time, for each of the four
ambient NO 2 monitors, shown in Figures E-3 through E-6. Both of these evaluations show improved model performance with the modified urban option in AERMOD.F-2 0.01

0.1

1 10

0.01 0.1 1 10PREDICTED

OBSERVED INDIANAPOLIS SF6 1-HR Q-Q PLOT (CONC) - All Stabilities

AERMOD v09292 AERMOD v11059

Figure E-1. 1-hour Q-Q Pl ot for Indianapolis SF 6 Study for All Stabilities

Figure E-2. 1-hour Q-Q Pl ot for Indianapolis SF 6 Study for Convective ConditionsF-3 Atlanta NO2 Study - 1-hr QQ Plot for Monitor 0002 - Urban Transition Adjustment

0 50 100 150 200

0 50 100 150 200 Observed Conc (ppb)Predicted Conc (ppb)

0002 - New 0002 - Old

Figure E-3. 1-hour Q- Q Plot for Atlanta NO 2 Study for Monitor 0002

Atlanta NO2 Study - 1-hr QQ Plot for Monitor 3001 - Urban Transition Adjustment

0 50 100 150 200

0 50 100 150 200 Observed Conc (ppb)Predicted Conc (ppb)

3001 - New 3001 - Old

Figure E-4. 1-hour Q- Q Plot for Atlanta NO 2 Study for Monitor 3001F-4 Atlanta NO2 Study - 1-hr QQ Plot for Monitor 0048 - Urban Transition Adjustment

0 50 100 150 200

0 50 100 150 200 Observed Conc (ppb)Predicted Conc (ppb)

0048 - New 0048 - Old

Figure E-5. 1-hour Q- Q Plot for Atlanta NO 2 Study for Monitor 0048

Atlanta NO2 Study - 1-hr QQ Plot for Monitor JST - Urban Transition Adjustment

0 50 100 150 200

0 50 100 150 200 Observed Conc (ppb)Predicted Conc (ppb)

JST - New JST - Old

Figure E-6. 1-hour Q- Q Plot for Atlanta NO 2 Study for Monitor JSTF-1 

### APPENDIX F. EV ALUATION OF LOW WIND BETA OPTIONS

Beginning with version 12345, AERMOD includes non-default BETA op tions to address concerns regarding model performance under lo w wind speed conditions. This includes the LOWWIND1 and LOWWIND2 BETA options on the MODELOPT keyword in AERMOD, and the ADJ_U* option included in Stage 3 of th e AERMET meteorological processor, beginning with version12345. Preliminary evaluation results for these BETA options in AERMOD are presented below, based on field studies conduc ted in 1974 by the Air Resources Laboratory of the National Oceanic and Atmospheric Administ ration (NOAA) to investigate diffusion under low wind speed conditions at Idaho Falls ( NOAA, 1974) and Oak Ridge (NOAA, 1976). These two field studies were used in the API-s ponsored evaluations of AERMOD conducted by AECOM (AECOM, 2009), that were subsequently submitted as part of API’s public comments on EPA’s 10 th Conference on Air Quality Models held in March 2012. The preliminary evaluation results presented here were based in part on the information included in the AECOM’s 2009 report and data files subse quently provided by AECOM. However, some adjustments were made based on an independent assessment of the surf ace roughness for each of the study locations, an adjustment to the effective tracer release height at Idaho Falls from 1.5 to 3m based on information provided on page 24 of the NOAA Technical Memorandum for Idaho Falls (NOAA, 1974), and adjustments to the wind measurement heights for Oak Ridge based on the discussion in Section 2.2 and information provided in Table 1 of the NOAA Technical Memorandum for Oak Ridge (NOAA, 1976). The AE COM evaluation for Oak Ridge used a 2m wind measurement height, whereas page 8 of th e NOAA report for Oak Ridge indicated that the wind measurements were “accomplished by laser anemometry” due to the fact that wind speeds were “below the threshold of standard cup anemom eters”. Footnotes in Table 1 also confirm that wind speeds were “measured by laser anemometers” for all tests, except for Test 11 where the wind speed was measured at the 30.5m level on one of meteorologi cal towers included in the study. Given the fact that the transmitters and r eceivers for the laser anemometer were located on the hills on either side of the valley where the tracer was released, at elevations between 50 to 100 feet higher than the elevati on at the release point (based on Figure 2b of the NOAA report), a 2m wind measurement height may not be a ppropriate. However, the NOAA report does not indicate an “effective” measurement height above ground for the wind speeds measured by the laser anemometers. Another aspect of the us e of laser anemometry that complicates the determination of an appropriate measurement hei ght is the fact that the “measured” wind speeds may represent more of a volume average than a point measurement. Based on these considerations, the preliminary evaluation results presented here were based on an “effective” wind measurement height of 10m, and the winds were also assumed to represent vector mean wind speeds. A series of figures is provided below for each site, starting with the Idaho Falls study followed by the Oak Ridge study. For each site a series of Q-Q plots, paired plots and residual plots are shown starting with the No ADJ_U*/No LowWind Option case, followed by ADJ_U*/No_LowWind Option; ADJ_U*/ LowWind1; and ADJ_U*/LowWind2.F-2 Idaho Falls: Q-Q Plot - He=3m - 0.08m Zo - No ADJ_U* - No LowWind Options - v12345 Obs (unfitted) vs AERMOD (Base 1-Layer, Scalar WS) Predicted Arc-Max @ 3 DW Arcs

0 50 100 150 200

0 50 100 150 200
Observed (  g/m 3 )Predicted (g/m3) 100-m Arc

200-m Arc

400-m Arc

Idaho Falls: Q-Q Plot - He=3m - 0.08m Zo - With ADJ_U* - No LowWind Options - v12345 Obs (unfitted) vs AERMOD (Base 1-Layer, Scalar WS) Predicted Arc-Max @ 3 DW Arcs

0 50 100 150 200

0 50 100 150 200
Observed (  g/m 3 )Predicted (g/m3) 100-m Arc

200-m Arc

400-m ArcF-3 Idaho Falls: Q-Q Plot - He=3m - 0.08m Zo - With ADJ_U* - LowWind1 Option - v12345 Obs (unfitted) vs AERMOD (Base 1-Layer, Scalar WS) Predicted Arc-Max @ 3 DW Arcs

0 50 100 150 200

0 50 100 150 200
Observed (  g/m 3 )Predicted (g/m3) 100-m Arc

200-m Arc

400-m Arc

Idaho Falls: Q-Q Plot - He=3m - 0.08m Zo - With ADJ_U* - LowWind2 Option - v12345 Obs (unfitted) vs AERMOD (Base 1-Layer, Scalar WS) Predicted Arc-Max @ 3 DW Arcs

0 50 100 150 200

0 50 100 150 200
Observed (  g/m 3 )Predicted (g/m3) 100-m Arc

200-m Arc

400-m ArcF-4 Idaho Falls: Paired Plot - He=3m - 0.08 Zo - No ADJ_U* - No LowWind Options - v12345

Obs (unfitted) vs AERMOD (Base 1-Layer, Scalar WS) Pred Arc-Max @ 3 DW Arcs

0 50 100 150 200

0 50 100 150 200
Observed (  g/m 3 )Predicted (g/m3) 100-m Arc

200-m Arc

400-m Arc

Idaho Falls: Paired Plot - He=3m - 0.08 Zo - With ADJ_U* - No LowWind Options - v12345 Obs (unfitted) vs AERMOD (Base 1-Layer, Scalar WS) Pred Arc-Max @ 3 DW Arcs

0 50 100 150 200

0 50 100 150 200
Observed (  g/m 3 )Predicted (g/m3) 100-m Arc

200-m Arc

400-m ArcF-5 Idaho Falls: Paired Plot - He=3m - 0.08 Zo - With ADJ_U* - LowWind1 Option - v12345

Obs (unfitted) vs AERMOD (Base 1-Layer, Scalar WS) Pred Arc-Max @ 3 DW Arcs

0 50 100 150 200

0 50 100 150 200
Observed (  g/m 3 )Predicted (g/m3) 100-m Arc

200-m Arc

400-m Arc

Idaho Falls: Paired Plot - He=3m - 0.08 Zo - With ADJ_U* - LowWind2 Option - v12345

Obs (unfitted) vs AERMOD (Base 1-Layer, Scalar WS) Pred Arc-Max @ 3 DW Arcs

0 50 100 150 200

0 50 100 150 200
Observed (  g/m 3 )Predicted (g/m3) 100-m Arc

200-m Arc

400-m ArcF-6 Idaho Falls: Resid Plot vs. DW Dist - He=3m - 0.08-Zo - No ADJ_U* - No LW Opts - v12345 Pred (AERMOD Base 1-Layer, S calar WS) vs Obs (unfitted)

0.01 0.10 1.00 10.00 100.00

100 - ns=11 200 - ns=11 400 - ns=11

Receptor ArcsPredicted / Observed

Idaho Falls: Resid Plot vs. DW Dist - He=3m - 0.08-Zo - With ADJ_U* - No LW Opts - v12345 Pred (AERMOD Base 1-Layer, S calar WS) vs Obs (unfitted)

0.01 0.10 1.00 10.00 100.00

100 - ns=11 200 - ns=11 400 - ns=11

Receptor ArcsPredicted / ObservedF-7 Idaho Falls: Resid Plot vs. DW Dist - He=3m - 0.08-Zo - With ADJ_U* - LW1 Option - v12345 Pred (AERMOD Base 1-Layer, S calar WS) vs Obs (unfitted)

0.01 0.10 1.00 10.00 100.00

100 - ns=11 200 - ns=11 400 - ns=11

Receptor ArcsPredicted / Observed

Idaho Falls: Resid Plot vs. DW Dist - He=3 m - 0.08-Zo - With ADJ_U* - LW2 Option - v12345 Pred (AERMOD Base 1-Layer, S calar WS) vs Obs (unfitted)

0.01 0.10 1.00 10.00 100.00

100 - ns=11 200 - ns=11 400 - ns=11

Receptor ArcsPredicted / ObservedF-8 Oak Ridge: Q-Q Plot - No ADJ_U* - No LowWind Options - v12345 Obs vs AERMOD (Base 1-Layer, Vector WS, 10m-Zref, 0.6m-Zo) Predicted Arc-Max @ 3 DW Arcs

0 500 1000 1500

0 500 1000 1500
Observed (  g/m 3 )Predicted (g/m3) 100-m Arc

200-m Arc

400-m Arc

Oak Ridge: Q-Q Plot - With ADJ_U* - No LowWind Options - v12345 Obs vs AERMOD (Base 1-Layer, Vector WS, 10m-Zref, 0.6m-Zo) Predicted Arc-Max @ 3 DW Arcs

0 50 100 150 200

0 50 100 150 200
Observed (  g/m 3 )Predicted (g/m3) 100-m Arc

200-m Arc

400-m ArcF-9 Oak Ridge: Q-Q Plot - With ADJ_U* - LowWind1 Option - v12345 Obs vs AERMOD (Base 1-Layer, Vector WS, 10m-Zref, 0.6m-Zo) Predicted Arc-Max @ 3 DW Arcs

0 100 200 300 400 500

0 100 200 300 400 500
Observed (  g/m 3 )Predicted (g/m3) 100-m Arc

200-m Arc

400-m Arc

Oak Ridge: Q-Q Plot - With ADJ_U* - LowWind2 Option - v12345 Obs vs AERMOD (Base 1-Layer, Vector WS, 10m-Zref, 0.6m-Zo) Predicted Arc-Max @ 3 DW Arcs

0 25 50 75 100

0 25 50 75 100
Observed (  g/m 3 )Predicted (g/m3) 100-m Arc

200-m Arc

400-m ArcF-10 Oak Ridge: Paired Plot - No ADJ_U* - No LowWind Options - v12345 Obs vs AERMOD (Base 1-Layer, Vector WS, 10m-Zref, 0.6m-Zo) Pred Arc-Max @ 3 DW Arcs

0 500 1000 1500

0 500 1000 1500
Observed (  g/m 3 )Predicted (g/m3) 100-m Arc

200-m Arc

400-m Arc

Oak Ridge: Paired Plot - With ADJ_U* - No LowWind Options - v12345 Obs vs AERMOD (Base 1-Layer, Vector WS, 10m-Zref, 0.6m-Zo) Pred Arc-Max @ 3 DW Arcs

0 50 100 150 200

0 50 100 150 200
Observed (  g/m 3 )Predicted (g/m3) 100-m Arc

200-m Arc

400-m ArcF-11 Oak Ridge: Paired Plot - With ADJ_U* - LowWind1 Option - v12345 Obs vs AERMOD (Base 1-Layer, Vector WS, 10m-Zref, 0.6m-Zo) Pred Arc-Max @ 3 DW Arcs

0 100 200 300 400 500

0 100 200 300 400 500
Observed (  g/m 3 )Predicted (g/m3) 100-m Arc

200-m Arc

400-m Arc

Oak Ridge: Paired Plot - With ADJ_U* - LowWind2 Option - v12345 Obs vs AERMOD (Base 1-Layer, Vector WS, 10m-Zref, 0.6m-Zo) Pred Arc-Max @ 3 DW Arcs

0 25 50 75 100

0 25 50 75 100
Observed (  g/m 3 )Predicted (g/m3) 100-m Arc

200-m Arc

400-m ArcF-12 Oak Ridge: Residual Plot vs. DW Dist - No AD J_U* - No LowWind Options - v12345 Pred (AERMOD Base 1-Layer, Vector WS, 10m-Zref, 0.6m-Zo) vs Obs

0.01 0.10 1.00 10.00 100.00

100 - ns=11 200 - ns=11 400 - ns=10

Receptor ArcsPredicted / Observed

Oak Ridge: Residual Plot vs. DW Dist - With ADJ_U* - No LowWind Options - v12345 Pred (AERMOD Base 1-Layer, Vector WS, 10m-Zref, 0. 6m-Zo) vs Obs

0.01 0.10 1.00 10.00 100.00

100 - ns=11 200 - ns=11 400 - ns=10

Receptor ArcsPredicted / ObservedF-13 Oak Ridge: Residual Plot vs. DW Dist - With ADJ_U* - LW1 Option - v12345 Pred (AERMOD Base 1-Layer, Vector WS, 10m-Zref, 0.6m-Zo) vs Obs

0.01 0.10 1.00 10.00 100.00

100 - ns=11 200 - ns=11 400 - ns=10

Receptor ArcsPredicted / Observed

Oak Ridge: Residual Plot vs. DW Dist - With ADJ_U* - LW2 Option - v12345 Pred (AERMOD Base 1-Layer, Vector WS, 10m-Zref, 0.6m-Zo) vs Obs

0.01 0.10 1.00 10.00 100.00

100 - ns=11 200 - ns=11 400 - ns=10

Receptor ArcsPredicted / Observed